Summer Fish Kill

swimming pondHow does a summer fish kill happen? Wow what a year, spring seemed to last forever and the rain seemed never ending. Then all the sudden the faucet was turned off and hasn’t turned back on again. At the same time the rain stopped it turned into summer temps’ and has been here since. Now we want rain for the gardens, crunchy brown grass, crops and of course the ponds are slowly getting smaller.

With the hot temperatures and lack of rain the water has warmed up as well, no need to “get use to it” just walk right in. Good for us but not the fish. You see they can stand some pretty warm temps’ and they will just slow down a little. The biggest thing to be concerned with is how much dissolved oxygen is in the water and to what depth does the oxygen reach?

Why does this matter? Fish need oxygen just like we do. But a pond without aeration or a poor aeration system does not get enough oxygen to the bottom of the pond where it is needed. Down at the bottom there is these guys called anaerobic bacteria. They live in the muck slowly eating away at it, they create some bad stuff. The “stuff” is toxic gasses to fish, ammonia, carbon dioxide, and hydrogen sulfide. These gasses accumulate at the bottom and build towards the surface, see what’s happening, the fish are being pushed to the surface for more oxygen.

display aeratorSeeing the fish at the surface of the pond gasping for air is the state of an emergency. For quick oxygen you could use a display aerator fountain or even a boat motor propeller partially in the water to break the surface tension and create oxygen. Bottom diffused aeration would not be for an emergency but actually a long term cure for the pond, the fish, water quality, muck reduction and pushing those bad gasses out of the pond.

A note of caution not all system are created equal. Some say good for an acre but what is the actual gallon per minute of water they are moving? Is the system turning over the entire water volume at least once a day? Same with the diffuser itself and the design so it is moving water off the bottom of the pond at the mud water interface where the oxygen is actually needed, to break down the muck and maximize oxygen content. Sure sound simple but wait a minute, let’s say the diffuser doesn’t affect or start moving water until 20”-24” or more from the bottom. If the pond is 20’ deep the fish maybe safe…but what if the pond is only 5’ deep? There is only 3’ left for the fish to try and breathe, but the gasses keep building and the warmer the water the less oxygen it holds.

This year has been bad for a lot of folks with summer fish kills. Some had no aeration while others did, which was due to the type of system, poor design or not sized properly. Why wait and take that chance of losing your fish. It is a sad day walking to the pond and seeing them all floating. Contact us with your pond location and we will work with you to calculate the proper aeration system to meet your pond and fish needs. See also the Pond Management page for a free MP3 download.

About the Author: Darrell Rhoades is the founder of and has great expertise in building ponds. It all started when he built his own pond for the family. He writes about pond management and sell pond management products at

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