Low oxygen content in water can be a prescription for disaster

Everyone who has a recreational farm pond enjoys the opportunity to step outside and catch fish. However, nothing can be more disheartening than to carefully nurture a pond only to discover a fish kill on a hot summer morning. The July/August 2006 issue of Kansas Wildlife & Parks magazine features an article by Pratt Fish Hatchery manager Mark Kumberg addressing this issue.

To prevent fish kills, a pond or lake must have one element to support fish and other higher organisms -- oxygen. Oxygen depletion is the most common cause of fish kills, and low oxygen occurs most often during periods of calm, cloudy, hot weather.
Most dissolved oxygen in water comes from the atmosphere on windy days and as a byproduct of aquatic plant photosynthesis. Less sunlight penetrates deeper water, reducing deeper water vegetation, thus reducing oxygen content at deeper strata.

Dissolved oxygen levels can also be affected by temperature. Colder water holds oxygen better, and very warm water easily loses oxygen. Atmospheric pressure is also a factor. Oxygen solubility increase as atmospheric pressure rises.

Most fish kills occur in the early morning before the sun comes up, when dissolved oxygen levels are lowest, and, unfortunately, larger fish are usually the first to be affected. Ponds or lakes with large amounts of algae or phytoplankton can have high oxygen during the day, but at night, these plants use up oxygen.

Herbicides or algaecides can help control aquatic vegetation and reduce the chances of a fish kill. However, this must be done carefully to prevent rapid decomposition and further oxygen depletion. Other ways to prevent oxygen depletion include pumping or flowing water into a pond, preventing runoff that adds nutrients to a pond, using a commercial aerator, reducing feed amounts if artificial feeding is used, and maintaining the proper fish density for the size of the pond.

More information on pond management is available here .

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