View source for Earth:Fish kill

{{Short description|Localized die-off of fish populations}}
[[File:Fish Kill 745F2A9C-65B8-D693-7ABA3282F6A1ECE4.jpg|thumb|300px|right|There are many causes of fish kill, but oxygen depletion is the most common cause.]]
The term '''fish kill''', known also as '''fish die-off''', refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.<ref>U.S. Environmental Protection Agency. Washington, DC (2000). [http://www.epa.gov/305b/98report/98brochure.pdf "The Quality of Our Nation’s Waters - A Summary of the National Water Quality Inventory: 1998 Report to Congress."] {{webarchive|url=https://web.archive.org/web/20080724052358/http://www.epa.gov/305b/98report/98brochure.pdf |date=24 July 2008 }} Document no. EPA-841-S-00-001. p. 18.</ref><ref name="autogenerated2005">University of Florida. Gainesville, FL (2005). [http://aquat1.ifas.ufl.edu/guide/fiskil.html "Fish kill."] {{webarchive|url=https://web.archive.org/web/20080924135959/http://aquat1.ifas.ufl.edu/guide/fiskil.html |date=24 September 2008 }} ''Plant Management in Florida's Waters.''</ref> The most common cause is reduced oxygen in the water, which in turn may be due to factors such as drought, [[Biology:Algae bloom|algae bloom]], overpopulation, or a sustained increase in water temperature. Infectious diseases and parasites can also lead to fish kill. [[Medicine:Toxicity|Toxicity]] is a real but far less common cause of fish kill.<ref>Noga, Fish Disease: Diagnosis and Treatment, 2010, John Wiley and Sons {{ISBN|0-8138-0697-6}}, p. 316</ref>

Fish kills are often the first visible signs of environmental stress and are usually investigated as a matter of urgency by environmental agencies to determine the cause of the kill. Many fish species have a relatively low tolerance of variations in environmental conditions and their death is often a potent indicator of problems in their environment that may be affecting other animals and plants and may have a direct impact on other uses of the water such as for drinking water production. Pollution events may affect fish species and fish age classes in different ways. If it is a cold-related fish kill, [[Biology:Juvenile fish|juvenile fish]] or species that are not cold-tolerant may be selectively affected. If [[Medicine:Toxicity|toxicity]] is the cause, species are more generally affected and the event may include amphibians and shellfish as well. A reduction in dissolved oxygen may affect larger specimens more than smaller fish as these may be able to access oxygen richer water at the surface, at least for a short time.

==Causes==
[[File:Scheme eutrophication-en.svg|thumb|300px|right|Depleted oxygen levels are the most common cause of fish kills. In this way eutrophication can have devastating consequences for the health of benthic life]]

Fish kills may result from a variety of causes. Of known causes, fish kills are most frequently caused by pollution from agricultural runoff or biotoxins. [[Earth:Hypoxia (environmental)|Ecological hypoxia]] (oxygen depletion) is one of the most common natural causes of fish kills. The suffocating event may be brought on by factors such as [[Biology:Algae bloom|algae bloom]]s, droughts, high temperatures<ref>Oregon State University (2006). [http://www.eurekalert.org/pub_releases/2006-10/osu-dhe103006.php "Deadly hypoxic event finally concludes"] {{webarchive|url=https://web.archive.org/web/20110314083456/http://www.eurekalert.org/pub_releases/2006-10/osu-dhe103006.php |date=14 March 2011 }},</ref> and [[Physics:Thermal pollution|thermal pollution]]. Fish kills may also occur due to the presence of disease, agricultural runoff, [[Earth:Sewage|sewage]] discharges, oil or hazardous waste spills, hydraulic fracturing wastewater, [[Earth:Earthquake|sea-quake]]s, inappropriate re-stocking of fish, [[Biology:Poaching|poaching]] with chemicals, underwater explosions, and other catastrophic events that upset a normally stable aquatic population.<ref name="autogenerated2005"/> Because of the difficulty and lack of standard protocol to investigate fish kills, many fish kill cases are designated as having an unknown cause.<ref>La, V. and S. J. Cooke. (2011). [http://vantla.com/wordpress/wp-content/uploads/2010/12/RFS-La-Cooke-2011.pdf "Advancing the science and practice of fish kill investigations."] {{webarchive|url=https://web.archive.org/web/20120425145844/http://vantla.com/wordpress/wp-content/uploads/2010/12/RFS-La-Cooke-2011.pdf |date=25 April 2012 }} Reviews in Fisheries Science. 19(1): 21-33.</ref><ref>Saraghan, M. (October, 2011). [http://www.scientificamerican.com/article.cfm?id=epa-scientist-points-at-fracking-in-fish-kill-mystery&page=3 EPA Scientist Points at Fracking in Fish-Kill Mystery.] {{webarchive|url=https://web.archive.org/web/20131213233127/http://www.scientificamerican.com/article.cfm?id=epa-scientist-points-at-fracking-in-fish-kill-mystery&page=3 |date=13 December 2013 }} Scientific American. Retrieved 8 September 2012.</ref>

===Oxygen depletion===
[[File:Dead and dying Cyprinus carpio carpio in Lake Albert.jpg|thumb|left|Dead and dying European carp in Lake Albert. Fish kills are often a sign of environmental stress.]]
Oxygen enters the water through [[Physics:Diffusion|diffusion]]. The amount of oxygen that can be dissolved in water depends on the [[Physics:Atmospheric pressure|atmospheric pressure]], the water temperature and whether the water is salty.<ref>[http://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html Oxygen Solubility in Fresh and Sea Water] {{webarchive|url=https://web.archive.org/web/20110103230758/http://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html |date=3 January 2011 }}. Engineeringtoolbox.com. Retrieved on 2012-05-23.</ref> For example, at 20&nbsp;°C (68&nbsp;°F) and one atmosphere of pressure, a maximum of 8&nbsp;mg/L of oxygen can dissolve in sea water (35&nbsp;mg/L [[Earth:Salinity|salinity]]) while a maximum of 9&nbsp;mg/L of oxygen can dissolve in fresh water. The amount of oxygen that can be dissolved in the water decreases by about 1&nbsp;mg/L for each 10&nbsp;°C increase in water temperature above 20&nbsp;°C.

Many cold water fish that live in clean cold waters become stressed when oxygen concentrations fall below 8&nbsp;mg/L while warm water fish generally need at least 5 ppm (5&nbsp;mg/L) of dissolved oxygen. Fish can endure short periods of reduced oxygen. Depleted oxygen levels are the most common cause of fish kills. Oxygen levels normally fluctuate even over the course of a day and are affected by weather, temperature, the amount of sunlight available, and the amount of living and dead plant and animal matter in the water.<ref name="BGWM">A Beginner's Guide to Water Management – Fish Kills, Information Circular 107, University of Florida IFAS Extension, 2003 [http://edis.ifas.ufl.edu/topic_fish_kills read online] {{webarchive|url=https://web.archive.org/web/20110504040737/http://edis.ifas.ufl.edu/topic_fish_kills |date=4 May 2011 }}</ref> In temperate zones oxygen levels in eutrophic rivers in summertime can exhibit very large [[Earth:Diurnal cycle|diurnal]] fluctuations with many hours of oxygen [[Physics:Supersaturation|supersaturation]] during daylight followed by oxygen depletion at night.<ref>[http://www.env.gov.bc.ca/wat/wq/BCguidelines/do/do-02.htm Ambient Water Quality Criteria for Dissolved Oxygen] {{webarchive|url=https://web.archive.org/web/20100811091231/http://www.env.gov.bc.ca/wat/wq/BCguidelines/do/do-02.htm |date=11 August 2010 }}. Env.gov.bc.ca. Retrieved on 2012-05-23.</ref> Associated with these photosynthetic rhythms there is a matching [[Chemistry:PH|pH]] rhythm as bicarbonate ion is metabolised by plant cells. This can lead to pH stress even when oxygen levels are high.

Additional dissolved organic loads are the most common cause of oxygen depletion and such organic loads may come from sewage, farm waste, tip/landfill [[Earth:Leachate|leachate]] and many other sources.

===Diseases and parasites===
[[File:Cadmans Pool, New Forest. - geograph.org.uk - 61031.jpg|thumb|right|This pond in New Forest, England, has been restored following a viral infection which killed all the fish.]]
Fish are subject to various [[Biology:Virus|virus]]es, [[Biology:Bacteria|bacteria]] and [[Biology:Fungi|fungi]] in addition to parasites such as protozoans, flukes and worms, or crustaceans. These are naturally occurring in many bodies of water, and fish that are stressed for other reasons, such as spawning or suboptimal water quality, are more susceptible. Signs of disease include sores, missing scales or lack of slime, strange growths or visible parasites, and abnormal behavior–lazy, erratic, gasping at the water surface or floating head, tail or belly up.

For example, since 2004 fish kills have been observed in the Shenandoah River basin in the spring, from the time water temperatures are in the 50s (°F) until they reach the mid-70s.  So far, investigators suspect certain bacteria, along with environmental and contaminant factors that may cause immune suppression.<ref>[http://www.deq.state.va.us/info/srfishkill.html information from the Department of Environmental Quality, Virginia, USA] {{webarchive|url=https://web.archive.org/web/20110524035958/http://www.deq.state.va.us/info/srfishkill.html |date=24 May 2011 }}; see also [http://www.deq.state.va.us/info/srfishkillhistory.html History of fish kills in the Shenandoah watershed, Virginia] {{webarchive|url=https://web.archive.org/web/20110524044853/http://www.deq.state.va.us/info/srfishkillhistory.html |date=24 May 2011 }}</ref>

In fish farming, where populations are optimized for the available resources, parasites or disease can spread quickly. In [[Biology:Channel catfish|channel catfish]] [[Biology:Aquaculture of catfish|aquaculture ponds]], for example, the "hamburger gill disease" is caused by a protozoan called ''Aurantiactinomyxon'' and can kill all the fish in an affected pond. In addition to altered behavior, affected fish have swollen gills that are mottled and have the appearance of ground hamburger meat.<ref name="BGWM"/>

Some early warning signs of fish suffering from disease or parasite infections include:<ref>[https://web.archive.org/web/20100610081128/http://pubs.ext.vt.edu/420/420-252/420-252.pdf Fish Kills - Their Causes and Prevention, Virginia Tech, Virginia Cooperative Extension Publication 420-252, 2009].</ref>
#Discolouration, open sores, reddening of the skin, bleeding, black or white spots on the skin
#Abnormal shape, swollen areas, abnormal lumps, or popeyes
#Abnormal distribution of the fish such as crowding at the surface, inlet, or pond edges (though crowding at the surface during specific times of day, such as early morning, is more likely a sign of low oxygen)
#Abnormal activity such as flashing, twisting, whirling, convulsions, loss of buoyancy
#Listlessness, weakness, sluggishness, lack of activity
#Loss of appetite or refusal to feed.

===Toxins===
Agricultural runoff, [[Earth:Sewage|sewage]], [[Earth:Surface runoff|surface runoff]], chemical spills and hazardous waste spills can all potentially lead to water [[Medicine:Toxicity|toxicity]] and fish kill. Some algae species also produce toxins. In Florida, these include ''[[Biology:Aphanizomenon|Aphanizomenon]]'', ''[[Biology:Anabaena|Anabaena]]'' and ''Microcystis''. Some notable fish kills in Louisiana in the 1950s were due to a [[Biology:Pesticide|pesticide]] called [[Chemistry:Endrin|endrin]].<ref>Larson et al., 1997, Pesticides in Surface Waters: distribution, trends and governing factors. CRC Press {{ISBN|1-57504-006-9}} p. 278</ref> Natural instances of toxic conditions can occur, especially in poorly [[Chemistry:Buffer solution|buffer]]ed water. Aluminium compounds can cause complete fish kills, sometimes associated with autumn turn-over of lakes leading to complex chemical interactions between pH, [[Chemistry:Calcium|calcium]] ions and complex polymeric salts of aluminium.<ref>[http://www.sekj.org/PDF/anzf33/anzf33-517p.pdf http://www.sekj.org/PDF/anzf33/anzf33-517p.pdf] {{webarchive|url=https://web.archive.org/web/20110828232501/http://www.sekj.org/PDF/anzf33/anzf33-517p.pdf |date=28 August 2011 }}. Retrieved on 2012-05-23.</ref>

Human-induced fish kills are unusual, but occasionally a spilled substance causes direct toxicity or a shift in water temperature or pH that can lead to fish kill.  For example, in 1997 a [[Chemistry:Phosphate|phosphate]] plant in Mulberry, Florida, accidentally dumped 
{{convert|60|e6USgal|e6kl|abbr=unit}} of acidic process water into Skinned Sapling Creek, reducing the pH from about 8 to less than 4 along {{convert|36|mi|km}} of creek, resulting in the death of about 1.3 million fish.<ref name="BGWM"/>

It is often difficult or impossible to determine whether a potential toxin is the direct cause of a fish kill.  For example, hundreds of thousands of fish died after an accidental spill of bourbon whiskey into the Kentucky River near Lawrenceburg. However, officials could not determine whether the fish kill was due to the bourbon directly or to oxygen depletion that resulted when aquatic microbes rapidly began to consume and digest the liquor.<ref name="BGWM"/>

[[Chemistry:Cyanide|Cyanide]] is a particular toxic compound that has been [[Earth:Cyanide fishing|used to poach fish]]. In cyanide poisoning the gills turn a distinctive cherry red. [[Chemistry:Chlorine|Chlorine]] introduced as alkaline hypochlorite solution is also extremely toxic,<ref>[https://web.archive.org/web/20110317032617/http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/202794/nsw-fish-kill.pdf Fish Kills in New South Wales]</ref> leaving pale mucilaginous gills and an over-production of mucilage across the whole body. [[Chemistry:Calcium oxide|Lime]] produces similar symptoms but is also often associated with milk eyes.

===Algae blooms and red tides===
[[File:River Cam green.JPG|thumb|right|A small algae bloom on River Cam near Trinity College]]
[[File:Cwall99 lg.jpg|thumb|right|A large algae bloom off the southern coast of England in 1999]]
[[File:Red tide.jpg|thumb|right|Red tide is a reddish algae bloom caused by a microorganism common in the Gulf of Mexico]]
An [[Biology:Algae bloom|algae bloom]] is the appearance of a large amount of [[Biology:Algae|algae]] or scum floating on the surface of a body of water. Algae blooms are a natural occurrence in nutrient-rich lakes and rivers, though sometimes [[Earth:Nutrient pollution|increased nutrient levels]] leading to algae blooms are due to fertilizer or animal waste runoff. A few species of algae produce [[Biology:Toxin|toxin]]s, but most fish kills due to algae bloom are a result of decreased oxygen levels. When the algae die, [[Medicine:Decomposition|decomposition]] uses oxygen in the water that would be available to fish. A fish kill in a lake in Estonia in 2002 was attributed to a combination of algae bloom and high temperatures.<ref>{{cite book|author=Estonian Academy Publishers|title=Proceedings of the Estonian Academy of Sciences, Biology and Ecology|url=https://books.google.com/books?id=zGqUHtmTCuoC&pg=PA67|year=2005|publisher=Estonian Academy Publishers|page=67}}</ref> When people manage algae blooms in fish ponds, it is recommended that treatments be staggered to avoid too much algae dying at once, which may result in a large drop in oxygen content.

Some diseases result in mass die-offs.<ref name="Moyle466">Moyle and Cech, 2004, page 466</ref> One of the more bizarre and recently discovered diseases produces huge fish kills in shallow marine waters. It is caused by the [[Biology:Ambush predator|ambush predator]] [[Biology:Dinoflagellate|dinoflagellate]] ''[[Biology:Pfiesteria piscicida|Pfiesteria piscicida]]''. When large numbers of fish, like [[Biology:Shoaling and schooling|shoaling]] [[Biology:Forage fish|forage fish]], are in confined situations such as shallow bays, the excretions from the fish encourage this dinoflagellate, which is not normally toxic, to produce free-swimming zoospores. If the fish remain in the area, continuing to provide nourishment, then the zoospores start secreting a [[Chemistry:Neurotoxin|neurotoxin]]. This toxin results in the fish developing bleeding lesions, and their skin flakes off in the water. The dinoflagellates then eat the blood and flakes of tissue while the affected fish die.<ref name="Burkholder">Burkholder JM, Glasgow HB and Hobbs CW (1995) [https://www.int-res.com/articles/meps/124/m124p043.pdf "Fish kills linked to a toxic ambush-predator dinoflagellate: distribution and environmental conditions"] {{webarchive|url=https://web.archive.org/web/20120223203635/https://www.int-res.com/articles/meps/124/m124p043.pdf |date=23 February 2012 }} ''Marine Ecology Progress Series''.</ref> Fish kills by this dinoflagellate are common, and they may also have been responsible for kills in the past which were thought to have had other causes.<ref name="Burkholder"/> Kills like these can be viewed as natural mechanisms for regulating the population of exceptionally abundant fish. The rate at which the kills occur increases as organically polluted land runoff increases.<ref>Magnien RE (2001) [http://www.bioone.org/doi/abs/10.1641/0006-3568(2001)051%5B0843:TDOSPA%5D2.0.CO%3B2 "The Dynamics of Science, Perception, and Policy during the Outbreak of Pfiesteria in the Chesapeake Bay"] ''BioScience'' '''51'''(10):843-852.</ref>

[[Biology:Red tide|Red tide]] is the name commonly given to an algal bloom of ''[[Biology:Karenia brevis|Karenia brevis]]'', a microscopic marine dinoflagellate which is common in Gulf of Mexico waters. In high concentrations it discolors the water which often appears reddish-brown in color. It produces a toxin which paralyses the central nervous system of fish so they cannot breathe. Dead fish wash up on beaches around Texas and Florida. Humans can also become seriously ill from eating oysters and other shellfish contaminated with the red tide toxin.<ref>{{cite web |url=http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/faq.phtml#q9 |title=Red Tide FAQ - Is it safe to eat oysters during a red tide? |publisher=Texas Parks and Wildlife Department |access-date= 2009-08-23 |url-status=live |archive-url=https://web.archive.org/web/20090706100608/http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/faq.phtml#q9 |archive-date=6 July 2009}}</ref><ref>{{cite web |url=https://www.cdc.gov/hab/redtide/ |title=Harmful Algal Blooms: Red Tide: Home |publisher=US Centers for Disease Control |access-date=2009-08-23 |url-status=live |archive-url=https://web.archive.org/web/20090509084035/http://www.cdc.gov/hab/redtide/ |archive-date=9 May 2009}}</ref>
The term "red tide" is also commonly used to describe harmful algal blooms on the northern east coast of the United States, particularly in the Gulf of Maine. This type of bloom is caused by another species of [[Biology:Dinoflagellate|dinoflagellate]] known as ''[[Biology:Alexandrium fundyense|Alexandrium fundyense]]''.<ref>{{cite web |url=http://www.mass.gov/?pageID=eohhs2modulechunk&L=4&L0=Home&L1=Provider&L2=Guidance+for+Businesses&L3=Food+Safety&sid=Eeohhs2&b=terminalcontent&f=dph_environmental_foodsafety_p_red_tide&csid=Eeohhs2
|title=Red Tide Fact Sheet - Red Tide (Paralytic Shellfish Poisoning) |publisher=Massachusetts Department of Public Health
|access-date  = 2009-08-23 |url-status=live |archive-url=https://web.archive.org/web/20090826001901/http://www.mass.gov/?pageID=eohhs2modulechunk&L=4&L0=Home&L1=Provider&L2=Guidance+for+Businesses&L3=Food+Safety&sid=Eeohhs2&b=terminalcontent&f=dph_environmental_foodsafety_p_red_tide&csid=Eeohhs2 |archive-date=26 August 2009}}</ref> These blooms are natural phenomenon, but the exact cause or combination of factors that result in red tides outbreak not fully understood.<ref>{{cite web
|url=http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/faq.phtml |title=Red Tide FAQ |publisher=Texas Parks and Wildlife Department |access-date=2009-08-23 |url-status=live |archive-url=https://web.archive.org/web/20090706100608/http://www.tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/faq.phtml |archive-date=6 July 2009}}</ref>

===Biological decay===
Just as an algae bloom can lead to oxygen depletion, introduction of a large amount of [[Medicine:Decomposition|decaying]] biological material in general to a body of water leads to oxygen depletion as [[Biology:Microorganism|microorganism]]s use up available oxygen in the process of breaking down [[Chemistry:Organic matter|organic matter]].  For example, a {{convert|10|mi|km}} fish kill in September, 2010, in the Sangamon River in Illinois was traced to discharge of animal waste into the river from a large dairy operation. The illegal discharge resulted in a complete kill of fish, frogs, [[Biology:Mussel|mussel]]s and mudpuppies.<ref>[http://www.pantagraph.com/news/local/contaminated-water-kills-fish-in-central-illinois/article_a64ef8bc-bf50-11df-9804-001cc4c002e0.html Contaminated Water Kills Fish in Central Illinois] {{webarchive|url=https://web.archive.org/web/20160415154155/http://www.pantagraph.com/news/local/contaminated-water-kills-fish-in-central-illinois/article_a64ef8bc-bf50-11df-9804-001cc4c002e0.html |date=15 April 2016}}</ref>

=== Nutrient pollution and eutrophication ===
[[File:Dead Zone NASA NOAA.jpg|thumb|Map of the dead zone in the Gulf of Mexico]]
Excessive anthropogenic [[Earth:Nutrient pollution|nutrient enrichment]] of phosphorus and nitrogen allow for rapid growth and multiplication of [[Biology:Algal bloom|phytoplankton]] in the Mississippi River. As phytoplankton continue to rapidly grow under optimal conditions, their biomass is almost doubled every 24 hours. In the water, higher concentrations of organic matter are present because of the high reproductive rate of the phytoplankton over a short period of time. The rapid growth of phytoplankton causes [[Biology:Turbidity|turbidity]] in the waters of the Mississippi and the Gulf of Mexico. Turbidity is defined as the measure of water clarity by how much the suspended material, such as algae and phytoplankton, constrict the passage of sunlight through water. Hence, as phytoplankton begin to multiply more rapidly, turbidity in the river and gulf increases.<ref name=":0">{{Cite book |title=Environmental Science: Toward a Sustainable Future |last1= Wright |first1= Richard T. |publisher=Pearson Education |year=2014 |location=Boston |pages=523–578 |last2=Boorse |first2=Dorothy F.}}</ref> The increasing turbidity blocks plants from absorbing sunlight. The process of turbidity results in limited photosynthesis production, and sometimes even death from sunlight deprivation of the submerged aquatic vegetation that are affected by the opaque turbid water accumulating at the surface.

Furthermore, a significant detrimental outcome caused by [[Earth:Eutrophication|eutrophication]] in the Mississippi River is the increased uptake of dissolved oxygen by bacteria, in response to higher concentrations of organic matter. After eutrophication starts and is in progress, the phytoplankton reach their maximum [[Earth:Population density|population density]] and begin to die.<ref name=":0" /> As the dead phytoplankton accumulate, detritus, or organic matter waste, forms at the surface along with other bacteria and algae. As more phytoplankton die, the higher the concentration of organic matter becomes; and with a higher concentration of organic matter, more bacteria will reproduce.

Consequently, as more bacteria, phytoplankton, and algae exponentially grow and multiply, the more submerged aquatic vegetation die, because they do not have access to sunlight due to eutrophication. Once this snowball-like course of action is in full motion, a dead zone has been created. As a result of the excess nutrient enrichment in the Mississippi River, dead zones appear in the Gulf of Mexico, created from the process of eutrophication. The dead zones in the gulf are mainly created by the nitrogen and phosphorus enrichment of the Lower Mississippi River.

===Spawning fatalities===
[[File:Dead salmon in spawning season.jpg|thumb|right|A salmon which has died after spawning]]
Some species of fish exhibit mass simultaneous mortality as part of their natural life cycle.
Fish kill due to spawning fatalities can occur when fish are exhausted from [[Biology:Spawn|spawning activities]] such as courtship, nest building, and the release of eggs or milt (sperm). Fish are generally weaker after spawning and are less resilient than usual to smaller changes in the environment.  Examples include the [[Biology:Atlantic salmon|Atlantic salmon]] and the [[Biology:Sockeye salmon|Sockeye salmon]] where many of the females routinely die immediately after spawning.

===Water temperature===
{{main|Physics:Thermal pollution}}
A fish kill can occur with rapid fluctuations in temperature or sustained high temperatures. Generally, cooler water has the potential to hold more oxygen, so a period of sustained high temperatures can lead to decreased dissolved oxygen in a body of water.  An August 2010 fish kill in Delaware Bay was attributed to low oxygen as a result of high temperatures.<ref>[http://www.newjerseynewsroom.com/science-updates/fish-kill-in-delaware-bay-still-a-mystery-to-nj-dep August 2010 fish kill in Delaware Bay linked to high temperatures – low oxygen] {{webarchive|url=https://web.archive.org/web/20100818072307/http://www.newjerseynewsroom.com/science-updates/fish-kill-in-delaware-bay-still-a-mystery-to-nj-dep |date=18 August 2010 }}. Newjerseynewsroom.com (2010-08-12). Retrieved on 2012-05-23.</ref>
A massive (hundreds of thousands) fish kill at the mouth of the Mississippi River in Louisiana, September, 2010, was attributed to a combination of high temperatures and low tide. Such kills are known to happen in this region in late summer and early fall, but this one was unusually large.<ref>[https://www.reuters.com/news/pictures/slideshow?articleId=USRTR2IDT7 Slideshow: Massive fish kill] {{webarchive|url=https://web.archive.org/web/20140222203924/http://www.reuters.com/news/pictures/slideshow?articleId=USRTR2IDT7 |date=22 February 2014 }} Reuter’s News Service report of massive fish kill at the mouth of the Mississippi River in September, 2010. The Division of Wildlife stated that the fish kill was unrelated to the oil spill that had recently occurred in the Gulf of Mexico: [http://www.aolnews.com/2010/09/16/massive-mississippi-river-fish-kill-not-bps-fault/ http://www.aolnews.com/2010/09/16/massive-mississippi-river-fish-kill-not-bps-fault/ Massive Fish Kill Not BP's Fault]  {{webarchive|url=https://web.archive.org/web/20121007233913/http://www.aolnews.com/2010/09/16/massive-mississippi-river-fish-kill-not-bps-fault/ |date=7 October 2012 }}</ref>

A short period of hot weather can increase temperatures in the surface layer of water, as the warmer water tends to stay near the surface and be further heated by the air.  In this case, the top warmer layer may have more oxygen than the lower, cooler layers because it has constant access to atmospheric oxygen. If a heavy wind or cold rain then occurs (usually during the autumn but sometimes in summer), the [[Earth:Stratification (water)|layers can mix]]. If the volume of low oxygen water is much greater than the volume in the warm surface layer, this mixing can reduce oxygen levels throughout the [[Earth:Water column|water column]] and lead to fish kill.

Fish kills can also result from a dramatic or prolonged drop in air (and thus, water) temperature. This kind of fish kill is selective – usually the dead fish are species that cannot tolerate cold. This has been observed in cases where a fish native to a more tropical region has been introduced to cooler waters, such as the introduction of the [[Biology:Tilapia|tilapia]] to bodies of water in Florida. Native to Africa's Nile River, the tilapia stop feeding when water temperatures drop below {{convert|60|°F|°C|abbr=on}} and die when it reaches {{convert|45|°F|°C|abbr=on}}. Thus, tilapia that have survived and successfully reproduced in Florida are occasionally killed by a winter cold front.<ref name="BGWM"/>

In January, 2011, a selective fish kill affecting an estimated 2 million juvenile spot fish was attributed to a combination of cold stress and overpopulation after a particularly large spawn.<ref>[http://www.cnn.com/2011/US/01/06/maryland.fish.kill/index.html?iref=obinsite CNN story on Jan 6, 2011 Fish kill in Maryland] {{webarchive|url=https://web.archive.org/web/20121109035058/http://www.cnn.com/2011/US/01/06/maryland.fish.kill/index.html?iref=obinsite |date=9 November 2012 }}. Cnn.com (2011-01-06). Retrieved on 2012-05-23.</ref>

"Hundreds of thousands" of fish were found dead in {{wipe|Texas}} in June 2023 due to warming water.<ref>{{Cite web |date=2023-06-15 |title=Hécatombe aux États-Unis : des milliers de poissons morts s'échouent sur les plages du Texas à cause de la chaleur de l'eau |url=https://www.tf1info.fr/international/etats-unis-golfe-du-mexique-des-milliers-de-poissons-morts-s-echouent-sur-les-plages-du-texas-a-cause-de-la-chaleur-de-l-eau-2260239.html |access-date=2023-06-19 |website=TF1 INFO |language=fr}}</ref>

===Underwater explosions===
[[Engineering:Underwater explosion|Underwater explosion]]s can lead to fish kill, and fish with [[Biology:Swim bladder|swim bladder]]s are more susceptible. Sometimes underwater explosions are used on purpose to induce fish kills, a generally illegal practice known as [[Biology:Blast fishing|blast fishing]]. Underwater explosions may be accidental or planned, such as for construction, [[Earth:Exploration geophysics|seismic testing]], mining or blast testing of structures under water.  In many places, an assessment of potential effects of underwater explosions on marine life must be completed and preventive measures taken before blasting.<ref>Lewis, 1996, Effects of Underwater Explosions on Life in the Sea, report DSTO-GD-0080 to the Australian Department of Defence [http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/3763/1/DSTO-GD-0080%20PR.pdf read online] {{webarchive|url=https://web.archive.org/web/20110706121631/http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/3763/1/DSTO-GD-0080%20PR.pdf |date=6 July 2011 }}; Govoni, et al., 2008, Effects of Underwater Explosions on Larval Fish: Implications for a Coastal Engineering Project, Journal of Coastal Research 2(S):228-233 {{doi|10.2112/05-0518.1}}</ref>

===Droughts and overstocking===
Droughts and overstocking can also result in inland fish kills.

A drought can lead to lower water volumes so that even if the water contains a high level of dissolved oxygen, the reduced volume may not be enough for the fish population.  Droughts often occur in conjunction with high temperatures so that the oxygen [[Earth:Carrying capacity|carrying capacity]] of the water may also be reduced. Low river flows also reduce the available dilution for permitted discharges of treated sewage or [[Earth:Industrial wastewater treatment|industrial waste]]. The reduced dilution increases the organic demand for oxygen further reducing the oxygen concentration available to fish

Overstocking of fish (or an unusually large [[Biology:Spawn|spawn]]) can also result in inland fish kills. Fish kill due to insufficient oxygen is really a matter of too much demand and too little supply for whatever reason(s).  Recommended stocking densities are available from many sources for bodies of water ranging from a home aquarium or backyard pond to commercial aquaculture facilities.
{{Clear}}

==Estimation==
Estimating the magnitude of a kill presents a number of problems.<ref name="Labay">{{cite journal |last1=Labay |first1=Andrew A. |last2=Bizan |first2=Dave |year=1999 |title=A Comparison of Fish Kill Counting Procedures on a Small, Narrow Stream |journal=North American Journal of Fisheries Management |volume=19 |issue=1 |pages=209–214 |publisher=American Fisheries Society |doi=10.1577/1548-8675(1999)019<0209:ACOFKC>2.0.CO;2  }}</ref>
#Polluted waters are often very [[Biology:Turbidity|turbid]] or have low transparency making it difficult or impossible to see fish that have sunk
#Rivers and streams can move fish downstream out of the investigation area.
#Small fish and fry can decompose or become buried in sediments very quickly and are lost from the count.
#Predators and [[Earth:Scavenger|scavenger]]s remove and eat fish.
#Stressed fish may swim up tributaries and die there
#Many kills are reported only when dead fish resurface due to decompositional gas formation, often several hours after the kill has occurred.
Some very large fish kills may never be estimated because of these factors. The discharge of red aluminium [[Engineering:Sludge|sludge]] from a reservoir in Hungary into the Marcai River is acknowledged as causing environmental devastation,<ref>
{{cite news |title=Hungarian chemical sludge spill reaches Danube |url=https://www.bbc.co.uk/news/world-europe-11491412 |newspaper=BBC News |date=2010-10-07 |url-status=live |archive-url=https://web.archive.org/web/20110120200728/http://www.bbc.co.uk/news/world-europe-11491412 |archive-date=20 January 2011}}</ref> The loss of adult fish also can have long-term impacts on the success of the fishery as the following year's [[Biology:Spawn|spawning]] stock may have been lost and recovery of the pre-kill population may take years. The loss of food supplies or recreational income may be very significant to the local economy.<ref>Environment Agency, UK (2009). [http://www.environment-agency.gov.uk/static/documents/Business/Preventing_fish_mortalities_-_Life_after_a_fish_mortality.pdf "Life after a fish mortality."] {{webarchive|url=http://webarchive.nationalarchives.gov.uk/20110203111515/http%3A//www.environment%2Dagency.gov.uk/static/documents/Business/Preventing_fish_mortalities_%2D_Life_after_a_fish_mortality.pdf |date=3 February 2011 }}</ref>

==Prevention and investigation==
Fish kills are difficult to predict. Even when conditions that contribute to fish kill are known to exist, prevention is hard because often conditions cannot be improved and fish cannot be safely removed in time. In small ponds, mechanical [[Earth:Water aeration|aeration]] and/or removal of decaying matter (such as fallen leaves or dead algae) may be reasonable and effective preventive measures.

Many countries in the developed world have specific provisions in place to encourage the public to report fish kills<ref>[http://research.myfwc.com/fishkill/submit.asp Florida Fish and Wildlife Research Institute - Submit A Fish Kill Report] {{webarchive|url=https://web.archive.org/web/20110405022446/http://research.myfwc.com/fishkill/submit.asp |date=5 April 2011 }}. Research.myfwc.com. Retrieved on 2012-05-23.</ref> so that a proper investigation can take place.<ref>Environment Agency, UK (2010-12-22). [http://www.environment-agency.gov.uk/research/commercial/40101.aspx "Fish mortality investigations."] {{webarchive|url=https://web.archive.org/web/20120314024852/http://www.environment-agency.gov.uk/research/commercial/40101.aspx |date=14 March 2012 }}</ref> Investigation of the cause of a kill requires a multi-disciplinary approach including on-site environmental measurements, investigation of inputs, review of meteorology and past history, toxicology, fish autopsy, invertebrate analysis and a robust knowledge of the area and its problems.<ref>Pierce, Robert A.; May, Thomas W.; Suppes, V. Charles (1994). [http://extension.missouri.edu/explorepdf/agguides/wildlife/g09402.pdf "Collection and Submission of Samples for Fish-Kill Investigation and Toxic-Substance Analysis."] University of Missouri Extension, Columbia, MO. Publication No. G9402.</ref>

==Notable events==
The counts given below are all estimates. They tend to be underestimates, and may omit, for example, small fish, those removed by scavengers and those that settle to the bottom.<ref name="Labay"/>
{| class="wikitable sortable"
|-
! Event/Location
! Date
! Count
! Species
! Remarks
<!-----------------------
This is an example to copy and paste:

|-
| [[Astronomy:Earth|Earth]]
| 2025 01
| {{sort|00001000|1,000}}
| [[Biology:Goldfish|goldfish]]
| Caused by a meteor<ref>http://www.examplereference.com {{Dead link|date=March 2022}}</ref>

(add it below this line:)
 ------------------------->
|-
| Gulf of Mexico (Corpus Christi)
| 1935
| {{sort|22000000|22,000,000}}
|
| Caused by [[Biology:Red tide|red tide]]. This event caused coughing, sneezing and watery red eyes in humans.<ref name=Reisinger>Reisinger, E. Anthony (2000). [http://www.utpa.edu/csl/redtide.html "Red Tide."] {{webarchive|url=https://web.archive.org/web/20101213033922/http://www.utpa.edu/csl/redtide.html |date=13 December 2010 }} Coastal Studies Laboratory, University of Texas-Pan American. Edinburg, TX.</ref>
|-
| River Aeron
| 1974
| {{sort|00010000|10,000}}
| salmon, [[Biology:Trout|trout]]
| Discharge of [[Engineering:Creamery|creamery]] waste through poorly maintained sewer. Successful prosecution followed.
|-
| River Neath
| 1976
| {{sort|00050000|50,000}}
| salmon, [[Biology:Trout|trout]]
| Extreme drought left fish stranded in stagnant pools into which sewers drained.
|-
| River Ogmore
| 1979
| {{sort|00050000|50,000}}
| salmon, [[Biology:Trout|trout]]
| Spillage of Kymene from a [[Engineering:Paper mill|paper mill]] on the River Llynfi a tributary of the Ogmore. Successful prosecution followed and substantial compensation.
|-
| Gulf of Mexico
| 1986
| {{sort|22000000|22,000,000}}
| [[Biology:Gulf menhaden|Gulf menhaden]], striped mullet, various other species<ref>Trebatoski, Bob (1988). [http://repositories.tdl.org/tamug-ir/bitstream/handle/1969.3/18723/10246-Observations%20on%20the%201986-1987%20Texas%20Red%20Tide%20(Ptychodiscus%20brevis).pdf?sequence=1 "Observations on the 1987-1987 Texas Red Tide (''Ptychodiscus brevis'')."] {{webarchive|url=https://web.archive.org/web/20110728083110/http://repositories.tdl.org/tamug-ir/bitstream/handle/1969.3/18723/10246-Observations%20on%20the%201986-1987%20Texas%20Red%20Tide%20%28Ptychodiscus%20brevis%29.pdf?sequence=1 |date=28 July 2011 }} Texas Water Commission, Austin TX. Report No. 88-02.</ref>
| Caused by [[Biology:Red tide|red tide]].<ref name=Reisinger />
|-
| Rhine River
| 1986 01
| {{sort|00500000|500,000}}
|
| Caused by spill from Swiss chemical warehouse<ref>[http://www.radford.edu/wkovarik/envhist/majorEvents.disasters.html Environmental History Timeline] {{webarchive|url=https://web.archive.org/web/20110103222307/http://www.radford.edu/wkovarik/envhist/majorEvents.disasters.html |date=3 January 2011 }}. Radford.edu. Retrieved on 2012-05-23.</ref>
|-
| Texas coast
| 1997–1998
| {{sort|21000000|21,000,000}}
| 
| Caused by a bloom of ''[[Biology:Karenia brevis|Karenia brevis]]''<!--species is correct (formerly known as Gymnodinium breve and Ptychodiscus brevis) --><ref>Science House (North Carolina State University). [http://www.science-house.org/nesdis/algae/background.html "Algae Blooms."] {{webarchive|url=https://web.archive.org/web/20101201025428/http://www.science-house.org/nesdis/algae/background.html |date=1 December 2010 }} ''Investigating the Ocean''. Accessed 2011-01-07.</ref><ref>Bushaw-Newton, K.L. and Sellner, K.G.(1999). [http://oceanservice.noaa.gov/websites/retiredsites/sotc_pdf/hab.pdf "Harmful Algal Blooms."] {{webarchive|url=https://web.archive.org/web/20110727002805/http://oceanservice.noaa.gov/websites/retiredsites/sotc_pdf/hab.pdf |date=27 July 2011 }} ''NOAA's State of the Coast Report.'' Silver Spring, MD: National Oceanic and Atmospheric Administration.</ref>
|-
| White River; West Fork, Indiana
| 1999
| {{sort|4800000|4,800,000}}
| 
| Caused by an automotive parts maker in Anderson, Indiana, which had discharged 10,000 gallons of the chemical HMP 2000 into the river.
|-
| River Dee (United Kingdom)
| 2000 07
| {{sort|00100000|100,000}}<ref>{{cite news | url=http://news.bbc.co.uk/1/hi/wales/876571.stm | work=BBC News | title=Pollution toll rises to 100,000 fish | date=2000-08-11 | url-status=live | archive-url=https://web.archive.org/web/20040705023646/http://news.bbc.co.uk/1/hi/wales/876571.stm | archive-date=5 July 2004}}</ref>
| salmon, [[Biology:Trout|trout]], perch
| Unconfirmed link to release of whey into river
|-
| [[Biology:2002 Klamath River fish kill|Klamath River]]
| 2002 09
| {{sort|00070000|70,000}}<ref>{{cite news |title=In Klamath Basin, politics trump science |author=Steve Pedery |url=https://news.google.com/newspapers?id=ZF5WAAAAIBAJ&pg=4994,751693 |newspaper=The Register-Guard |date=2007-07-05 |access-date=25 May 2011}}</ref>
| salmon
| Low flow of water due to drought and water diversions for agriculture led to heated and shallow water, increasing vulnerability to a gill disease.
|-
| Neuse River, North Carolina
| 2004 09
| {{sort|01900000|1,900,000}}
| [[Biology:Menhaden|menhaden]]
| "Natural upwelling" of an acknowledged polluted river. Hydrogen sulfide smell reported<ref>{{cite news |title=Neuse fish kill estimate now closer to 2 million |first=Sue |last=Book |url=http://www.newbernsj.com/articles/neuse-47734-fish-million.html |newspaper=Sun Journal |location=New Bern, NC |date=2009-09-04 |url-status=live |archive-url=https://web.archive.org/web/20110727155840/http://www.newbernsj.com/articles/neuse-47734-fish-million.html |archive-date=27 July 2011}}</ref>
|-
| [[Earth:Taal Lake|Taal Lake]], Luzon, Philippines
| 2008 01 05
| {{sort|00010000|50 metric tons}}
| [[Biology:Tilapia|tilapia]]
| May be linked to volcanic activity and large fish farms
|-
| Liuxihe River Guangzhou People's Republic of China
| 2008 09 09
| {{sort|00010000|10,000}}
| carp
| Unknown<ref>Chinadaily.com.cn. "[http://www.chinadaily.com.cn/china/2008-09/12/content_7020664.htm Chinadaily.com.cn] {{webarchive|url=https://web.archive.org/web/20121023144838/http://www.chinadaily.com.cn/china/2008-09/12/content_7020664.htm |date=23 October 2012 }}." ''Dead fish mystery in Guangzhou probed.'' Retrieved on 2010-01-08.</ref><ref>hk.apple.nextmedia.com. "[http://www1.hk.apple.nextmedia.com/template/apple/art_main.php?iss_id=20080911&sec_id=15335&art_id=11585511 hk.apple.nextmedia.com] {{webarchive|url=https://web.archive.org/web/20110714181512/http://www1.hk.apple.nextmedia.com/template/apple/art_main.php?iss_id=20080911&sec_id=15335&art_id=11585511 |date=14 July 2011 }}." ''廣州流溪河污染　魚屍數萬條.'' Retrieved on 2010-01-08.</ref>
|-
| Beaches at Thanet, Kent, England
| 2010 01
| {{sort|00010000|20,000}}
| [[Biology:Velvet crab|velvet crab]]
| 20000 + dead crabs – along with dead starfish, lobsters, sponges and anemones. Probably killed by [[Physics:Hypothermia|hypothermia]].<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/england/kent/8456514.stm |title=Thousands of dead crabs wash up on Kent beaches |work=BBC News |date=13 January 2010 |access-date=10 January 2011}}</ref><ref>[http://thanetcoastlife.blogspot.com/2011/01/winter-crab-deaths-statistics-and.html ''Winter Crab deaths - the statistics and a ramble'' - Thanet coast life] {{webarchive|url=https://web.archive.org/web/20110708065354/http://thanetcoastlife.blogspot.com/2011/01/winter-crab-deaths-statistics-and.html |date=8 July 2011 }} Retrieved on 2011-01-08</ref>
|-
| Ting River Fujian People's Republic of China
| 2010 07
| {{sort|01000000|>1,000,000}} Enough to feed 70,000 people a year<ref>National geographics. "[http://news.nationalgeographic.com/news/2010/12/101221-next-water-pollution-disasters-/ National Geographic] {{webarchive|url=https://web.archive.org/web/20101225112609/http://news.nationalgeographic.com/news/2010/12/101221-next-water-pollution-disasters-/ |date=25 December 2010 }}." ''Water pollution disaster.'' Retrieved on 2010-01-08.</ref>
| 
| Part of the Zijin mining disaster<ref name="bloom1">Bloomberg.com. "[https://www.bloomberg.com/news/2010-12-28/zijin-mining-officials-fined-1-16-million-yuan-for-waste-spills-in-fujian.html  Bloomberg.com] {{webarchive|url=https://web.archive.org/web/20140304120438/http://www.bloomberg.com/news/2010-12-28/zijin-mining-officials-fined-1-16-million-yuan-for-waste-spills-in-fujian.html |date=4 March 2014 }}." ''Zijin mining officials fined 1.16 million yuan for waste spills in fujian.'' Retrieved on 2010-01-08.</ref>
|-
| Mississippi River; Plaquemines Parish, Louisiana
| 2010 09
| {{sort|00100000|100,000}}<ref>{{cite news |title=Massive La. Fishkill Prompts Oil Spill Questions Hundreds of Thousands of Dead Fish in Bayou Near Mississippi River; Oil, Chemical Dispersant, Oxygen Levels Eyed as Culprits |url=http://www.cbsnews.com/stories/2010/09/15/national/main6868602.shtml |quote=Hundreds of thousands of dead fish were floating west of the Mississippi River, in Bayou Chaland. |newspaper=CBS News |date=15 September 2010 |access-date=2011-01-07 |url-status=live |archive-url=https://web.archive.org/web/20110120114351/http://www.cbsnews.com/stories/2010/09/15/national/main6868602.shtml |archive-date=20 January 2011}}</ref>
| redfish, [[Biology:Trout|trout]], [[Biology:Flounder|flounder]]
| 
|-
|Arkansas River; Ozark, Arkansas
| 2010 12
| {{sort|00100000|100,000}}<ref name="CNN1">{{cite news|url=http://edition.cnn.com/2011/US/01/02/arkansas.fish.kill/index.html|title=Massive fish kill blankets Arkansas River|quote=Dead drum fish floated in the water and lined the banks of a 20-mile stretch of the Arkansas River near Ozark, about 125 miles northwest of Little Rock, said Keith Stephens of the Arkansas Game and Fish Commission. A tugboat operator discovered the fish kill Thursday night, and fisheries officials collected some of the dying animals to conduct tests. ...|date=3 January 2011|work=CNN|access-date=4 January 2011|url-status=live|archive-url=https://web.archive.org/web/20110104085200/http://edition.cnn.com/2011/US/01/02/arkansas.fish.kill/index.html|archive-date=4 January 2011}}</ref>
| [[Biology:Freshwater drum|freshwater drum]]
| Coincided with death of 5,000 [[Biology:Red-winged blackbird|red-winged blackbird]]s that fell from the sky.
|-
| Chesapeake Bay
| 2011 01
| {{sort|02000000|2,000,000}}
| spot croakers
| Included some juvenile croakers. Cold water stress was believed to be the cause.<ref>Maryland Department of the Environment, Baltimore, MD (5 January 2011). [http://www.mde.state.md.us/programs/PressRoom/Pages/010511.aspx "MDE Investigates Large Fish Kill in Chesapeake Bay."] {{webarchive|url=https://web.archive.org/web/20110109002334/http://www.mde.state.md.us/programs/PressRoom/Pages/010511.aspx |date=9 January 2011 }} Press release.</ref>
|-
| Jiaxing Xiuzhou District People's Republic of China
| 2011 01 06
| {{sort|00250000|250,000}}
| bream, carp, murrel, [[Biology:Silver carp|silver carp]], [[Biology:Grass carp|grass carp]]
| Fish caught and transported to market held in large fish tanks fed with river water. Very rapid die-off and loss exceeded 100 tonnes.  Only fish caught from a river under China National Highway 320 east died.<ref>News.big5.enorth.com.cn. "[http://news.big5.enorth.com.cn/system/2011/01/07/005539358.shtml News.big5.enorth.com.cn] {{webarchive|url=https://web.archive.org/web/20110707015030/http://news.big5.enorth.com.cn/system/2011/01/07/005539358.shtml |date=7 July 2011 }}." ''嘉興一水產市場2.5萬斤魚暴斃 或有人投毒.'' Retrieved on 2010-01-08.</ref><ref>Tech-food.com. "[http://www.tech-food.com/news/2011-1-7/n0473675.htm Tech-food.com] {{webarchive|url=https://web.archive.org/web/20110111065159/http://www.tech-food.com/news/2011-1-7/n0473675.htm |date=11 January 2011 }}." ''浙江嘉兴市水产批发市场约2.5万斤鱼死亡.'' Retrieved on 2010-01-08.</ref>
|-
| Redondo Beach, California
| 2011 03
| {{sort|01000000|millions}}
| anchovies, [[Biology:Mackerel|mackerel]], sardines and other small fish
| Caused by oxygen deprivation<ref>[http://www.msnbc.msn.com/id/41972653/ns/us_news-environment/?GT1=43001 msnbc.com] {{webarchive|url=https://web.archive.org/web/20110311000826/http://www.msnbc.msn.com/id/41972653/ns/us_news-environment/?GT1=43001 |date=11 March 2011 }}. MSNBC. Retrieved on 2012-05-23.</ref>
|-
| [[Earth:Taal Lake|Taal Lake]], Batangas, Philippines
| 2011 05 29
| {{sort|00010000|750 metric tons}}
| [[Biology:Tilapia|Tilapia]], [[Biology:Milkfish|milkfish]]
| Caused by oxygen deprivation and large fish farms
|-
| Lingayen Gulf, Anda, Pangasinan, Philippines
| 2011 05 30
| {{sort|00010000|500 metric tons}}
| [[Biology:Milkfish|Milkfish]]
| Oxygen depletion and change of water climate
|-
| Nordreisa, Troms, Norway
| 2011 12 31
| several tons
| [[Biology:Herring|herring]]
|<ref>{{Cite news |author= Lofstad, Ralf |title= Over natta var stranda full av død sild |trans-title=Overnight the beach was full of dead herring |url= http://www.dagbladet.no/2012/01/02/nyheter/dyrenes_nyheter/innenriks/fiskedod/19632870/ |work= Dagbladet |language= no |date= 2 January 2012 |access-date= 2 January 2012 |url-status= live |archive-url= https://web.archive.org/web/20120107091519/http://www.dagbladet.no/2012/01/02/nyheter/dyrenes_nyheter/innenriks/fiskedod/19632870/ |archive-date= 7 January 2012}}</ref><ref>{{Cite news |title= Mass death of herring off northern Norway puzzles locals |url= http://www.monstersandcritics.com/news/europe/news/article_1683583.php/Mass-death-of-herring-off-northern-Norway-puzzles-locals |archive-url= https://archive.today/20120914161505/http://www.monstersandcritics.com/news/europe/news/article_1683583.php/Mass-death-of-herring-off-northern-Norway-puzzles-locals |url-status= dead |archive-date= 14 September 2012 |work= Monsters & Critics |agency= Deutsche Presse-Agentur |date= 2 January 2012 |access-date= 2 January 2012 }}</ref>
|-
| Guangxi, People's Republic of China 
| 2012 01 15
| 40 metric tons
| Various
| Caused by 2012 Guangxi cadmium spill<ref>[http://www.chinadaily.com.cn/cndy/2012-02/04/content_14536059.htm Officials fired over cadmium spill|Nation] {{webarchive|url=https://web.archive.org/web/20120206103615/http://www.chinadaily.com.cn/cndy/2012-02/04/content_14536059.htm |date=6 February 2012 }}. chinadaily.com.cn (2012-02-04). Retrieved on 2012-05-23.</ref>
|-
|Menindee Lakes, NSW, Australia
|2018 12
|1,000,000
|Murray cod, silver perch, golden perch, bony herring, carp
|An independent assessment found that three significant fish death events were primarily caused by local hydrological and climatic conditions, shaped by a broader climatic, hydrologic and basin management context that placed the lower Darling River at risk of such fish deaths. The immediate cause was oxygen depletion when the weir pool destratified.<ref>{{Cite report |last=Vertessy |first=Robert |last2=Barma |first2=Daren |last3=Baumgartner |first3=Lee |last4=Mitrovic |first4=Simon |last5=Sheldon |first5=Fran |last6=Bond |first6=Nicholas |date=2023-02-08 |title=Independent Assessment of the 2018-19 fish deaths in the lower Darling - Final Report |url=https://opal.latrobe.edu.au/articles/report/Final_report_of_the_Independent_Assessment_of_the_2018-19_fish_deaths_in_the_lower_Darling/16869591/2 |language=en |doi=10.26181/16869591.v2}}</ref>
|-
|Oder river, {{wipe|Poland}}
|2022
|10+ metric tons
|various: zander, [[Biology:Catfish|catfish]], [[Biology:Gudgeon (fish)|gudgeon]], [[Biology:Loach|loach]], chub, etc.
|2022 Oder environmental disaster
|-
|Menindee, NSW, Australia
|2023 03 17
|Millions
|Mostly bony herring
|Oxygen depletion<ref>{{Cite web |last=CSIRO |title=Expert commentary: Menindee fish kill |url=https://www.csiro.au/en/news/news-releases/2023/expert-commentary-on-menindee-fish-kill |access-date=2023-04-10 |website=www.csiro.au |language=en}}</ref>
|-
|Brazoria County, Texas, USA
|2023 06 13
|Tens of thousands 
|
|Oxygen depletion<ref>{{Cite web |last=AP |title=Tens of thousands of dead fish wash up on Texas beach due to low oxygen levels in water |url=https://amp.abc.net.au/article/102474300|access-date=2023-07-13 |website=amp.abc.net.au |language=en}}</ref>
|}

==See also==
* Aflockalypse
* [[Earth:Aquatic biomonitoring|Aquatic biomonitoring]]
* Bird kill
* Fish-kill tree
* [[Earth:Harmful algal bloom|Harmful algal bloom]]
* Mass mortality event
* Paramoebiasis
* [[Biology:Roadkill|Roadkill]]
* Sentinel species

==References==
{{Reflist|30em}}

==External links==
{{external media
|float=right
|width=240px
|video1=[https://web.archive.org/web/20110604121445/http://video.google.com/videoplay?docid=-1295443816859346212 Red tide outbreak and fish kill]
}}
* Herring, and Scott (2002) [http://earthobservatory.nasa.gov/Features/oman/ ''Fish Kill in the Gulf of Oman: A space-based diagnosis''] [[Organization:NASA|NASA]]: Earth Observatory, featured article.
*[http://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html Oxygen Depletion in Ponds, University of Georgia Cooperative Extension Service, Publication L233, 1993]
*[https://web.archive.org/web/20100610081128/http://pubs.ext.vt.edu/420/420-252/420-252.pdf Fish Kills – Their Causes and Prevention, Virginia Tech, Virginia Cooperative Extension Publication 420-252, 2009]

{{Diversity of fish|state=expand}}
{{Fish disease topics}}

[[Category:Water pollution]]

{{Sourceattribution|Fish kill}}