An insurance policy for future fish


The Clear Lake Aeration System is a tool to increase the concentration of dissolved oxygen to address symptoms of eutrophication.  This simply means the lake has too many nutrients.  Often caused by runoff from the land, the vegetation grows wild causing death of animals (fish) due to lack of oxygen.

According to “The aerators are designed to reduce the chance of a winter fish kill due to low oxygen levels in the lake. Oxygen is not injected into the water with the aeration system, but an exchange of oxygen occurs when the air hits the open water. The aerators create open areas where fish can go when oxygen levels start to decline.”

In the winter of 1978-1979, Clear Lake suffered a devastating loss of sport fish.  About 6 years later, the oxygen level dipped to critically low levels again.  This time, we were fortunate, and the fish population survived.

Fisheries Biologist for the Iowa DNR, Scott Grummer, emphasizes the importance of winter aeration in Clear Lake.

“Winter aeration is in place to help protect one of Iowa’s most popular recreation destinations, Clear Lake.  The fishery is a valuable resource for anglers, but it also plays a vital role in Clear Lake’s water quality.  A winter fish kill can upset the healthy balance in a fishery, leading to high densities of rough fish (Common Carp), which have negative consequences to water quality. This scenario happened in 1979 fish kill and the lake took over 30 years to get back to the well-balanced fishery we see today.”

In 1986, Clear Lake installed two aeration systems.  One is located on the east shore near downtown.  The other is on the northwest shoreline between Venetian Village and the Baptist Camp.  Their purpose is to reduce the disturbing trend of low dissolved oxygen levels during the winter months.  The hope?  Keep the fish population alive and thriving.

These systems have operated for the past 35 years on Clear Lake with no winter kill.

So, how do they work?

Typically, the aerators run when the lake is fully iced over, and the temperature is consistently below freezing.  How it actually works is very simple.  An air pump forces air down through a hose into the water, which typically sends bubbles to the surface.  The constant movement allows for open water as ice is not able to form around the movement.  When the air hits open water, oxygen levels increase. It is also a place for fish to go to receive an adequate amount of oxygen.

Unfortunately, there is no level of adjustment on these devices.  They are meant to run for the duration of the winter.

A common complaint from Clear Lakers isn’t the fact that aerators are being used to keep the fish population healthy.  Instead, it is mostly about placement of the aeration systems.

While the present location for the east aerator was the optimum site in 1986, there has been more vocal push-back in recent years.  As Clear Lake continues to grow and become a Midwest Destination in North Iowa, some residents believe that particular area of the lake – even in the winter – should be utilized for winter activities and events.

Others disagree, stating the fish population should be the key focus.

Scott Grummer provided a list of criteria for aeration location placement.

Clear Lake Aeration System Location criteria:

1) aeration systems must be spatially separated to create refuge areas in different locations

2) northern half of the lake takes advantage of NW winds

3) mechanical buildings are located on shore and are noisy, so they need to be located away from residences

4) short distance to deeper water (downtown location is very close to deep water when looking at lake depth contours)

5) previous oxygen depletion events started in the SE corner of the lake, moved north-northwest, and eventually worked west towards Ventura.  Refuge locations need to be along this path not at the beginning or end of these previous trends, if history would repeat itself.

An ISU CARD Survey in 2009 estimated the Lake generates $66 million annually, and the number 1 reason for visitation on Clear Lake was fishing.  The system was installed using Sport Fish Restoration Funds, with the electrical and maintenance costs funded by the state Fish & Game Trust Fund.

The DNR has been asked to be open to the idea of moving the aerator.  Two alternatives – Clear Lake State Park & McIntosh Woods State Park – have been deemed available in the past.

Regardless of where they are located, it’s safe to say they are a vital piece of keeping Clear Lake’s fish population healthy and thriving.

We know it’s a touchy subject, and that we’ve opened a can of worms with this blog post.  Whatever “side” of the argument you hold concerning the aeration system, please understand the importance of keeping our lake healthy and the fish alive.

It’s like an insurance policy, if you will, for the future of Clear Lake.