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DNR: Smell on Clear Lake likely from an algae bloom
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DNR: Smell on Clear Lake likely from an algae bloom


After many complaints made in the past few days about a strong sewer-like odor around Clear Lake, the Clear Lake Sanitary District (CLSD) reached out to the DNR to investigate.

Clear Lake travel - State Park beach

The DNR's most recent water sample shows Clear Lake State Park is OK for swimming.

During the investigation, DNR staff and CLSD staff checked flow data and other records, and inspected both wastewater lift stations located on the north shore and found everything to be working properly with no reports of any leaks or sewer-like odors.

Today, DNR staff reported a significant amount of decaying aquatic vegetation, primarily Curly Leaf Pondweed, along the north shore. DNR staff also reported a blue green algae bloom, which is potentially also causing the sewer-like odors.

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Blue green algae, or cyanobacteria blooms can cause clear water to become cloudy or covered in a scum layer, according to the Iowa DNR's website. The cloudy or scummy water often smells bad. Algal blooms usually float to the surface and can be many inches thick, especially near the shoreline. Blue green algae often form in warm, slow moving waters that are rich in nutrients, such as fertilizer runoff. Algal blooms can appear quickly and can last a few hours, days or weeks. Blue green algae can produce toxins that can cause people to get sick. Not all algal blooms produce toxins, however.

Routine water sampling has verified there is not a sewer leak in Clear Lake. The DNR and CLSD will continue to work together to monitor the situation.

The most recent water sample data taken by the DNR on June 7 indicates both state park beaches, Clear Lake and McIntosh Woods, showed the water there was OK for swimming. 


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