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We are seeing algae in Round Lake. Is the treatment responsible for this?

June 24, 2022

We sometimes hear questions or concerns from several sources at the same time about current conservancy or environmental topics in the Clear Lake Township.

Q: We are seeing algae in Round lake. Is the treatment responsible for this?

A: Scott from Aquatic Enhancement & Survey. Parts of Round Lake, especially the eastern (downwind) shore, have a good bit of filamentous algae building up along the shoreline based on the photos you shared. We don't usually see an increase in filamentous algae (sometimes commonly called pond scum) in response to natural lake treatments like we performed at Round Lake but it's certainly possible the treatment contributed to a normal occurrence of this algae buildup. While filamentous algae is unsightly and can be a nuisance, it is not considered a health threat to people or animals.

Filamentous algae generally grows on the lake bottom like green fur on a normal basis. It often becomes buoyant when gas bubbles are trapped in it. After it hits the surface, prevailing winds can move it to the downwind side of the lake where it gathers along the shoreline. Usually this is a short-term situation as weather conditions and growth patterns break up the algae on the shoreline. Generally, the shoreline will return to normal as the season progresses.

It’s important to know that I receive phone calls every year from people with filamentous algae accumulating along their shoreline where they had never noticed it before. It's pretty common for this to happen both on lakes that are treated and also on untreated lakes.

It's normal to have a temporary decrease in water clarity following a treatment for aquatic plants. Decomposing plants release nutrients which can spur the growth of filamentous algae. You also might have a decrease in water clarity as a result of organic acids being released from the plants as they decompose. How noticeable these effects are depends on the size of the treatment relative to the size and volume of the lake and other factors. Because we treated a relatively large portion of Round Lake, I would expect the natural results I’ve described to be more noticeable there compared to the larger Clear Lake.

Thank you to all those who reached out to the Conservancy with questions and concerns. We appreciate the opportunity to learn and share with our community.

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