Thousands of Fish Die as Heat Rises & Algae Blooms

While many people jump in the lake to keep cool, living life underwater isn’t always enough to protect fish from the heat.

Many people throughout the US have noticed fish struggling at the water surface and washing up onto their shore.  This is due to the heat wave that has hovered over the Midwest over the past few weeks.

Fish kills are actually common and do happen every summer, its part of the natural cycle. 

Oxygen levels have reached an all time low.  Low oxygen levels combined with high water temperatures cause fish kills that sometimes have people convinced their lakes have been poisoned.

Fish kills have resulted in a lot of calls and emails to local Fish & Wildlife Services, and the problem is widespread.  Even hardy fish species have succumbed to water temperatures above 90 degrees, especially fish that have spawned recently and are still recovering from stress.

High temperatures decrease the amount of dissolved oxygen in the water and also encourage the growth of algae that use up even more oxygen during the hours of dark when photosynthesis stops.  Lack of oxygen in water is made worse by extreme heat because water, when it gets hot, physically cannot hold as much oxygen as when it is cooler.  This change can occur very quickly.

Biologists say the hot weather has killed tens of thousands of fish including sturgeon, bass, catfish and carp.  These fish are victims of the drought during one of the warmest summers in history. The Federal U.S. Drought Monitor show nearly two-thirds of the lower 48 states are experiencing some form of drought, more than 3,000 heat records were broken over the past few weeks.

Even though it may look like a lot of fish on the water surface, complete fish kill in a single body of water is rare.  Normally, big fish are affected first because they require more oxygen than small fish.  Small fish will then repopulate the water.  In areas with complete fish kill, some management would be needed to bring them back. Residents can report fish kills in their location by contacting their local Fish & Wildlife Service or DNR.

Prevention is hard because often conditions cannot be improved and fish cannot be safely removed in time. In small ponds, aeration and mechanical removal (Water Weed Rake) of pond muck (dead algae, weeds, leaves etc.) and algae may be a reasonable and effective preventive measure.  Regular application of beneficial bacteria (AquaClear Pellets) will reduce the amount of pond muck.

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