Pond Boss Forums INTRO Questions & Observations IWhy is the lake so clear without aeration?

This goes contradictory to every thing that I have read. Two years ago the board of directors told me to turn of the five aerators that we had going in a 25.4 acre lake. After telling them that I thought they were wrong and why they shouldn't do it they did it anyway. I then quit my job as lake manager telling them if they could do it better it was all theirs. I just came back from a weekend at the lake and I can't believe it. The lake is clear down to about two feet the weeds are starting to grow around the edges like we wanted it to do. (Strickly a fishing lake we wanted some weeds for cover and food for the little fish) And I have to say it looks real good. What gives??????

I'll let the experts give you a better answer but I can tell you this. Aeration is a tricky thing, if the system is not designed property, if the diffusers are not placed properly, and the if system is not run properly, the the system can do harm rather than do good. I'm not saying that these factors applied to you, I'm just saying we have seen instances here on Pond Boss in which ponds were muddied up and fish kills were caused (or perhaps contributed to) by an improperly designed and/or used aeration system.

But wait to hear from someone that actually knows what they are talking about.

You're going to have to give more details if you want something other than a wag.
What's the lake shape & depth?
Where were the aerators positioned & what type? Did they run 24/7?
How much inflow/outflow & source?
What was water clarity before turning off aerators?
How long did it take for the lake to clear & what was the water clarity measured with a disk?
Was it muddy or green?
Why did they want them turned off?

A lot of myths are present about the affects of aeration. Many talk about affects of aeration, sell it, and do not really understand the limnology of the receiving water body. Too much generalization occurs without knowing details.

Without a lot of specific details no one can truly answer your questions. Lakes are very dynamic and constantly changing even though on the surface they appear fairly constant. Things are dying, getting eaten and regrowth occurs daily. When changes are obvioius then major shifts have occurrred. Aeration creates changes. A lot of other natural factors and interactions create changes. Together all contribute to the current status of the lake/pond. Water clarity and the stuff in water is always changing based on growth of plankton and its dynamics. Aeration or lack of it can affect nutrient availability. Rainfall / watershed and wind can affect nutrient availability and turbidity. Nutrient shifts and concentrations are responsible for creating the rise and fall of the plankton community. Without some before and after data of the plankton populations and the suspended detrital biomass not much can be said about the shift in water clarity of your BOW. Plankton densities are not the only things that contributes to water clarity. Frequently ponds and smaller lakes can go in a few days or weeks from very clear water of 8-12ft to transpariencies of 2-3 ft even during continuous aeration. Normally plankton blooms and suspended detritus are responsible for most the water turbidity.

Here are some of the answers to the questions

1 The lake is an odd shape. The best way to describe it is it is like an isosceles triangle with a lot of fingers. The small end of the triangle would be the deep end 20 feet. That end had 2 diffusers in it parallel to each other. The rest of the five diffusers were in the middle of the lake in 15-12 feet of water staggered out. The pumps were 2-3/4 and 3-1/3 HP vane pumps. Six of the diffusers were vertex air stations and one was a MixAir Twister diffuser. The oxygen was checked with a Sentry 3 meter. The worst reading that I last took were in 8/13/2006 10:45 AM. They were.


Depth Temp Oxygen
1 89 6
5 85 4
10 85 3.5
15 85 3.5
20 85 3.5

The pumps ran 24-7 from when the water got 65 degrees surface temp in the spring till late November when they were shut off except when we had ice on the lake then only one ran in the shallow part of the lake ran to keep it open. Then was shut off when the ice cleared

2 The in flow and out flow I cannot answer. It had a 6x6 overflow and in the spring sometime sounded like a water fall. The only water came in from the flow from the hills around the lake. The lake is surrounded by trees. One time was down about 28 inches before the fall rains. Was always full in the spring.

3 The water clarty before was starting to clear up we had a lot of colonial and blue algae. You could see down I am guessing about 8-10 inches and now it is about 2 feet. No disc to check.

4 I believe it started getting a little better last year.

5 Green

6 They just told me that they wanted to try is without them on.

Hello John,

Bill gave a great response to what dynamics occur in a water body. With your readings being so old (8/2006) we can assume much has changed.

Even with those readings, I would make an educated guess that the Biochemical and Chemical Oxygen Demands are not met and the Reduction Oxidation Potential is still reading negative thereby allowing the phosphates, nitrates, iron and other nutrients to be relased.

Now with the system off, I would say there is most likely a thermocline building preventing the mix and circulation for right now. The clarity is a result of this happening. Unfortunately by turning off the system, the zone for plankton algae growth and zooplankton population is greatly reduced and the desire to have a great fishery on this lake is greatly reduced. The concern will be in the fall when the lake will potentially go through its fall turnover. If this anoxic zone on the bottom is fairly large, the potential of a fish kill is increased.

I would suggest a resent water sampling be conducted to determine Dissolved oxygen, phosphates, nitrates, pH, Temperature and if possible, BOD (Biochemical Oxygen Demand). There are other test that can be done but those will be a great start to determine the Trophic state of the lake and its health.

A doctor would not give you a prognosis without blood test, x-rays or even a MRI, just as we can't give a prognosis without the lake's blood test (water samples) x-ray (DO profile) or MRI (BOD analysis).

Whether patterns play a great role in the equation and have been anything but stable or consistent the last 4 years. This year has been the coldest, wettest Summer to date in our area, and that has changed the typical dynamics of pretty much every pond and lake one way or the other.

There are sooo many factors and key components of lake management that are totally outside of your or anyones direct control.

Good Points Nate.