Summertime Pond Problem

We have received several calls in our office with concerns of fish kills in area ponds.  Fish kills can result from a variety of causes but the most common are weather, pond vegetation, and the interaction of the two. Oxygen is essential to aquatic life and should be maintained at levels of 4ppm (parts of oxygen per million parts of water) or higher. 

Ponds may become choked with vegetation because of the amount of rain we have been receiving in the last several weeks.  The reason for the early bloom is because of the nutrients or runoff of topsoil from the pond watershed.  

In July and August during daylight hours, vegetation will grow and produce high amount of oxygen to compensate for plant respiration and decomposition.  Problems may arise during hot, cloudy days. The lack of sunshine and airflow prevents the production for oxygen in the pond. The largemouth bass are the first to be affect because of their size. As the conditions improve the oxygen levels will rise and the fish kill will end. 

The problem of vegetation can be controlled with herbicides.  The pond owner should treat their pond in parts rather than the entire pond.  If you treat the whole pond, all of the vegetation will die-off at one time causing a substantial build-up of organic material decaying in the warm water and requires large amounts of oxygen to complete. Oxygen consumption far outpaces oxygen production and oxygen levels begin to decline significantly.  Couple this with a calm, cloudy day or two, and the pond owner will find dead fish floating on the pond surface.    

A pond can have a turnover during summer if conditions are present. The conditions are a warm, upper layer of water on top of a colder, bottom layer.  In a heavy rain event (several inches in just a few hours), the cold rainwater plunges through the warm upper layer towards the bottom.  This is because cold water is denser than warm water and therefore sinks.  This causes the entire pond to mix. When the water mixes, the water may become oxygen-deficient, resulting in a fish kill.  The most effective way to prevent summer fish kill is to install an aeration system. 

Our office can provide information about aeration systems and companies that will install a system for you. Call 419-281-7645 if you have any pond questions.