8/21/2007

Hot Summer Weather Taking a Toll on Fish in Some Farm Ponds

Calls from farm pond owners to the Iowa Department of Natural Resources about fish kills has been on the increase with the recent hot weather.

"These reports of summer fish kills is not surprising. The hot summer weather has created high water temperatures which is stressful to aquatic plants and algae which can lead to summer fish kills," said Chris Larson, fisheries supervisor for the DNR in southwest Iowa.

"When vegetation dies, the bacteria feeding on the decaying plants use oxygen to the point where low oxygen areas of the pond are not suitable for fish and some die. Usually larger fish are more susceptible to dying from low oxygen; however some smaller fish can be affected as well," Larson said. "The important thing to remember is that these partial summer kills rarely kill all the fish in the pond and in a couple of years the pond will be back in balance."

It is not uncommon to see hundreds of dead fish from a large summer kill, but there are still many more live fish still in the pond. An Iowa farm pond can support 500 to 600 pounds of fish per acre of water and most of fish in a pond weigh less than a few ounces. If a pond owner has a fish kill of less than a couple of hundred fish and there appears to be no apparent reason, for example nearby aerial spraying or recent heavy rainfall causing runoff, it is more than likely from a natural phenomenon such as summer kill.

Some measures that can help reduce the chances of summer kills include; pond deepening, watershed protection measures such as buffer strips and sediment basins, and livestock exclusion.

For additional information on farm pond management visit with your local Iowa DNR fisheries biologist.