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What is Pond Stratification and Its Effects on My Pond?

Anyone who has been swimming in a lake or deep pond in the summer has probably felt noticeably cooler water around his or her legs. This sensation was most likely caused by stratification of the water.

Stratification means that two significantly different layers of water have formed in the pond or lake. This usually occurs in the summer when the daily heat will warm the surface of the pond causing that water to become lighter and float above the cooler deeper water. That specific moment when you were swimming and you felt that sudden change in temperature was the thermo-cline, which signifies the exact spot where the warm water and cool water separate.

Pond stratification is significant because what essentially happens is part of the pond becomes unusable to aquatic life. The lower, cooler portion of the pond becomes void of oxygen and thus unable to process and break down waste and muck on the pond bottom, which creates an anorexic environment filled with toxic gases and poor water. This in and of itself does not cause many problems, however it is when the pond/ lake turns over that serious problems can occur.

Pond turnover is when the water on the bottom of the pond mixes with the lighter warmer water above it. This usually (naturally) takes place in the fall and is a result of the upper water layer cooling off and sinking in with the lower water. Pond turnover is also caused by significant amounts of rainfall that can also suddenly change the temperature of the surface water causing it to mix with the cooler water.



Turnover is usually characterized by foul odors emitting from the pond and the water appearing to be churned up. The odors are a result of the hydrogen sulfide from the bottom being released and the churned up appearance by the muck that has been lifted from the bottom into the water column. The turning over of a pond often times leads to a fish kill due to the fact that so much oxygen has been depleted and that the normally healthy water column where the fish live is now contaminated with the toxins from the bottom of the pond

The best way to guard against stratification and turnover in a pond or lake is a properly sized and well-placed aeration system. The only real aeration option for this scenario is a bottom-based diffuser system. This type of aeration system utilizes an air compressor to force air through tubing down to the bottom of the pond where it is released by the air diffusers in the form of tiny bubbles that float up to the pond surface.

This bubbling effect, while also adding oxygen to the pond, provides a mixing effect that eliminates stratification and creates uniform aeration and temperature stability from top to bottom fueling beneficial pond bacteria . The pond is now able to efficiently process and handle organic waste and muck and also protect against turnover and fish kills.

The one thing to note when adding an aeration system like this is that it must be turned on gradually, meaning it is not to be installed and immediately run 24/7. This will actually cause a turnover. The key is to gradually work up to full operation with short runs for a week or two, with regular increases in the time you let it run until it can run continuously or as long as needed without turning the water over. Most aeration systems come with instructions for this.

The bottom line is, if you can keep the water moving from top to bottom, you can prevent stratification and protect against turnover and the unnecessary fish kills that can result and once you get the right system in place you have a big building block in place for years of healthy water.

Casey Coke is a Marketing Manager for Natural Environmental Systems, L.L.C, a global supplier of microbial solutions for pond and lake management. The company markets their own brand of pond supplies under the registered brand name of Pond Keeper as well as various pond aerators .