Bill Dance Outdoors
Bill's Blog


Posted: July 31st, 2009 by Bill Dance

No doubt about it, the dog days of summer are here and not only are the day time temperatures scorching, the water temps are beginning to boil a little, too. This is the time of year when we hear quite a bit about “fish kills” in many local ponds and small lakes. It’s not uncommon then for these type waters to form a strata or “thermocline.” Imagine a pond or small lake that’s 20 feet deep. The thermocline will usually form at about 10 feet. This means that the carrying capacity of the lake is reduced to 50%. In other words, every living thing in the lake that depends on dissolved oxygen – such as fish, zooplankton and phytoplankton – - now lives in the upper 50% of the water column. Why? Simply because below the thermocline, there’s no dissolved oxygen!

Because warm water holds less oxygen, as the summer water temperatures increase, oxygen levels continue to decrease – this is a critical time, especially when you get several cloudy days and a cold rain. Because cold water is heavier than warm water, it hits the surface and falls through the warmer layers to below the thermocline forcing the bottom water upwards. The result is an undesirable event that most fishermen realize as a fish kill caused by “summer turn over.”

Three natural ways that small waters get oxygen are:

1) A flow through (a high volume of water running through the lake).
2) Wind Diffusion (which provides minimal oxygen) , and
3) Sunlight, which is the number one source. It creates photosynthesis through plant life, phytoplankton, etc.

When problems start to arise on ponds and small lakes, there are usually warning signs and you should always watch out for these symptoms:

- Unsightly algae caused by runoff or high nutrient levels.
- Fish kills, as mentioned before, caused by stagnant water and poor circulation.
- Foul odors resulting from hydrogen sulfide and other gases caused by insufficient oxygen and lack of circulation.
- Poor water clarity caused by high nutrient levels.
- Muck accumulation – without oxygen dead plant and animal matter can’t be quickly decomposed.
- Excessive mosquito and midge fly populations thrive in stagnate waters and low oxygen conditions

Now, there is a way to prevent these problems, and for me, that means using a good bottom aeration system. My preference is the one made by Vertex which creates a vertical current using the rising force of millions of small bubbles to entrain the water column, circulating the entire lake and allowing oxygen to be absorbed at the lake’s surface. It’s a beneficial and cost effective method of improving both the water quality of your lake and its overall health. By moving the lower-oxygen water up from the bottom and eliminating thermal stratification, oxygen levels throughout the water column are increased. Wide swings in oxygen are stabilized, preventing fish kills. Aeration also improves sport fisheries by allowing fish to expand their territory into formerly oxygen-deprived portions of the lake. With appropriate aeration, fish are no longer trying to survive in a stressful environment, but are instead thriving, happy and anxious to strike and eat your lures.

Bill Dance


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