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Fish Kills: Mother Nature's Plague

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August 24, 2012
Fish Kills: Mother Nature's Plague - 2

Fish kills are, in most cases, the result of reduced dissolved oxygen. However, fish kills can occur, with less frequency, from diseases and the occasional parasite infestation.

Any number of factors can diminish dissolved oxygen levels. Typically, these include drought, algae blooms, overpopulation, and elevated water temperature. In many cases, a combination of these factors can negatively affect the fragile ecosystem.

Dissolved oxygen levels drop during summer months when water temperatures rise. The algae living in a particular body of water require oxygen to survive. While algae produces oxygen during the day through photosynthesis, they consume oxygen without replacing it during the night. If enough algae is present, they can lower oxygen levels below the tolerance of fish (as they need less to survive than fish). Once that happens, the fish suffocate and die. And contrary to popular belief, most fish kills occur during the night.

Algal blooms, as they are referred to, occur both naturally and with the help of man — most commonly, the addition of nutrients into the water such as nitrogen and/or phosphorus are the problem.

Nutrients can come from several sources. Runoff from farming fertilizing operations is the common culprit. However, nutrients can also be introduced from something as simple as residents washing their cars with liquid soaps and detergents — they can make their way into ecosystems via storm water runoffs.

When these detrimental nutrients are introduced into the water shed, the growth of algae is accelerated, producing the “bloom.” Fish are typically the most susceptible residents of an ecosystem to these lowered dissolved oxygen levels — so they die first. For ecologists, a fish kill sends up a red flag that an ecosystem is unhealthy and in need of attention before any more damage is inflicted on the fragile eco-balance.

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from peteyraymond wrote 1 year 33 weeks ago

Tuesday Stine - The park warden may have been trying to discourage public urination (and the related indecent exposure violation), but I'm highly skeptical that fishermen's urine could cause a fish die off. Seems to me that it would take an extraordinary amount of urine to kill fish. It would probably take hundreds of fisherman per acre of water to have any effect. That many fishermen would make the lake unfishable anyway.

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from Tuesday Stine wrote 1 year 33 weeks ago

Interesting article. It makes me wonder, when you mention algae blooms with the help of man, can a large number of people, using food bait in a pond, cause too much waste build-up, in turn cause algae bloom? My brother had an algae bloom, which killed some fish, in his pond. He was feeding them and apparently his girls were helping out, without his knowledge. Also, a few years back a park warden approached our boat, while talking, he mentioned that the lack of fish in the lake was due to a large amount of urine from fishermen, causing massive die off of fish. I don't swim in that lake anymore!

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from Tuesday Stine wrote 1 year 33 weeks ago

Interesting article. It makes me wonder, when you mention algae blooms with the help of man, can a large number of people, using food bait in a pond, cause too much waste build-up, in turn cause algae bloom? My brother had an algae bloom, which killed some fish, in his pond. He was feeding them and apparently his girls were helping out, without his knowledge. Also, a few years back a park warden approached our boat, while talking, he mentioned that the lack of fish in the lake was due to a large amount of urine from fishermen, causing massive die off of fish. I don't swim in that lake anymore!

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from peteyraymond wrote 1 year 33 weeks ago

Tuesday Stine - The park warden may have been trying to discourage public urination (and the related indecent exposure violation), but I'm highly skeptical that fishermen's urine could cause a fish die off. Seems to me that it would take an extraordinary amount of urine to kill fish. It would probably take hundreds of fisherman per acre of water to have any effect. That many fishermen would make the lake unfishable anyway.

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