News & Events

Why are we seeing so many dead fish?

August 9, 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: Ann from the West Shore: Any idea what is causing so many fish to die in the lake? We just removed floating fish from our shoreline.

A.: Bridget: We communicated with Matt Horsley, our district fisheries biologist with the Indiana Department of Natural Resources to understand what caused the fish kill and to get answers to several other questions from community members.

Matt shared that about 400 - 500 dead fish, mostly rock bass and other sunfish, were observed. With the type of species impacted, Matt said this was a shallow water event likely caused by depleted oxygen levels.

Matt explained that he only saw a couple of fish in Marina Bay so he speculates it occurred out in the bigger part of the lake. He noticed that the shallow area between the north basin and south basin is heavily vegetated (not Eurasian watermilfoil). The plants are topped out in several areas covering quite a few acres. With the hot weather, warm water temperatures and calm (no wind) days, Matt suspects that this area is being sucked of oxygen every night by the plants and the fish are not able to find their way out with the vast size of the area.

IDEM and Law enforcement are all aware of the situation and Matt shared that he highly doubts it is from anything other than natural causes.

Q: This seems like a lot of fish! How will this impact the rock bass species?
A: Matt: The kill was likely localized to a smaller area so it will not impact the population as a whole.

Q: Is it safe to swim?
A: Matt: Yes, there aren't any concerns with swimming in the lake.

Q: Can the fish be eaten?
A: Matt: Freshly caught fish can be eaten.

Q: Should the dead fish be removed from the lake? Do they harm the lake water quality if left?
A: Matt: Dead fish washed up can be aesthetically unpleasing and smelly so they can be removed and discarded. It will not reduce overall water quality if left.

Q: Was this the result of the treatment of the Eurasian watermilfoil on June 1st?
A: Matt: I wouldn't suspect this to be related at all.

Q: Was this caused by an algae bloom?
A: Matt: I did not see any signs of an algae bloom when I visited on August 4th.

Members of the Conservancy's volunteer Water Quality Committee completed monthly water testing on Wednesday, August 3rd. Results did not indicate any cause for alarm. Additionally, we are gathering data through our Watershed Diagnostic Study. Building a robust collection of data will enable us to identify and plan the best and most effective projects to improve the water quality for the Clear Lake Watershed. Read more about this project here >>.

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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