DNR Biologist Weighs in on What Causes Summer Fish Kills

(Lewis) Iowa Department of Natural Resources Fisheries Biologist John Lorenzen is receiving reports of dead fish floating or washing up on shore in private ponds. Although concerning, Lorenzen says that most fish kills at this time of year occur naturally in shallow systems full of vegetation or algae.

Lorenzen says shallow systems have less water volume and are usually warmer. The warmer the water, the less oxygen it can hold.

Lorenzen says the smaller, younger fish take less oxygen and may survive.

*Note: The presence of tadpoles or frogs is a sign there are no fish in the pond. He says if a complete fish kill occurs in your pond, it’s time to consider what to change and then restock the pond.