Farm pond summer fish kill

Fish die from a variety of causes and a few dead fish floating on the surface of the farm pond isn’t necessarily a cause for alarm. But if there are a lot of dead fish and you see others gulping for air at the surface, you’ve got to find the cause.

Charlie Lee is an extension wildlife specialist at Kansas State University. He says fish kills come from improper use of aquatic herbicides, runoff from crop fields, or a sudden turnover in the pond water layers. However, the most common culprit is excess vegetation on the surface of the water, especially when the weather is hot, cloudy, and calm.

"It’s the plants that produce the oxygen during the day while there’s sunlight, but they’re not producing at night. And most of the oxygen in a pond is there as a result of plant photosynthesis," says Lee. "So most of our fish kills are a direct result of low dissolved oxygen."

Lee says you’re risking a fish kill if more than half of the surface is covered with vegetation and algae. Another less obvious problem might be planktonic algae.

"That’s the very small microscopic plants that are in the pond that typically gives the water its color, whether it’s green or brownish in color. They’re almost too small to see," he says. "But if you can’t see more than 12” into your pond and it’s due to planktonic algae and not soil particles, then you probably have a pond that’s too rich and producing too much planktonic algae."

The best solution is prevention by controlling algae and using some kind of aerator. But Lee says once you see fish at the surface gulping for air, it’s probably too late.