Field Notes

May 24, 2024

Toxic blue-green algae bloom identified on Big Chapman Lake

Read Time: 2 minutes

This week, the Lilly Center for Lakes & Streams identified a highly toxic blue-green algae (cyanobacteria) bloom in Big Chapman Lake. As a result, the Lilly Center urges lake residents to exercise caution and look for tell-tale signs of a blue-green algae bloom such as an oil spill-like appearance. When in doubt, stay out!

Thanks to a tip from a Chapman Lake resident, Lilly Center researchers conducted an analysis of microcystin, a blue-green algae toxin, in the lake to identify any potential threats.

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Lilly Center scientists collect water samples on Big Chapman Lake

The Indiana Department of Environmental Management’s threshold for pet safety is 0.8 parts per billion (ppb) and 8.0 ppb for human safety. Initial lab results from water samples in the north channel of Nelly’s Bay indicated a toxin level of 160.4 ppb. Further tests showed that the bloom had dissipated somewhat and dropped to 1.7 ppb.

However, toxin results from a second channel in Nelly’s Bay showed a microcystin concentration of 41.3 ppb. Although the visible bloom may begin to dissipate in the coming days, toxins may linger.

Lake residents are encouraged to stay out of the water in those channels and to keep their pets out of the water until after the bloom has disappeared.

The main body of Big Chapman Lake had microcystin levels below the pet and human safety threshold.

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Water samples are analyzed in the Lilly Center lab for toxins

Spotting a blue-green algae bloom is easy if you know the signs. A bloom will often have a pea soup or paint spill-like appearance and often be bright green or blue. Performing the “stick test” will help you identify the difference between harmless green algae and potentially toxic blue-green algae. Green algae is stringy and will hang off the stick, but blue-green algae will simply stir like paint.

If you spot a blue-green algae bloom or something you cannot identify, report it to the Lilly Center by emailing or calling 574-372-5281.

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Blue-green algae lookalikes

How do I prevent blooms?

There are a few ways to help limit blooms. This is what the Indiana Department of Natural Resources (IDEM) suggests:

  • Most established lawns do NOT need phosphorus to be healthy. If applying fertilizer, use a phosphorus-free lawn fertilizer. This is critical if you live on a lake. Lawn-fertilizer packaging is labeled with three numbers for nutrient content. A zero as the middle number indicates a phosphorus-free fertilizer.
  • Do not over fertilize in your garden. Check soil nutrient levels prior to applying garden fertilizer to ensure correct application. Soil test kits can be purchased from some local hardware stores and through online distributors.
  • Do not fertilize up to the edge of a waterway. Check with your local government for any specific setback requirements.
  • Do not dispose of grass clippings or leaves in or near a waterway.
  • To prevent inputs from human waste, have your septic system inspected and tank pumped out at least every two years.
  • If conducting land disturbing activity, prevent soil and organic matter from washing into waterways, as soil can carry nutrients into the waterway.
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Stay safe on the lake this summer!

Supported by the K21 Health Foundation and the Kosciusko County Convention, Recreation, and Visitor Commission, the Lilly Center conducts weekly sampling on 14 lakes and at seven public beaches throughout Kosciusko County. Samples are processed in the Lilly Center’s lab, and results are posted to our website each Friday, beginning June 7th.

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