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Cedar Lake near Nashua experiencing natural fish kill

The Iowa Department of Natural Resources (DNR) received a report of dead fish floating in Cedar Lake, an impoundment on the Cedar River near Nashua on Aug. 19th. 

A DNR investigation found several dead channel catfish.  A natural algae bloom was occurring in the lake at the time.  Mid-day dissolved oxygen readings were extremely high (over 18 mg/l), typical of algal blooms; however, no elevated ammonia levels were documented.

Algae blooms can produce very high oxygen levels during the day, but rapidly deplete dissolved oxygen levels at night as the algae die, suffocating bottom-dwelling fish such as catfish. 

“Recent cloudy, cool weather combined with low river levels have extended the natural algae die-off,” said Mike Siepker, DNR fisheries management biologist. “Lake users may continue to occasionally see dead or stressed fish.”

Fish caught from the lake are still safe to eat.

If you see dead fish when you are at a lake or river, call the DNR’s 24-hour spill line at 515-725-8694 as soon as possible. Quick reporting can help DNR staff identify the cause of a fish kill and potentially stop a fish kill in progress.

For more information, contact the Decorah Fisheries Management Office at 563-382-8324 or the Environmental Protection Field Office in Mason City at 641-424-4073.

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