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Public health warning issued for Lake Mitchell

Lake Mitchell was placed at warning level on Friday when readings showed that, on average, chlorophyll levels in the water were nearly four times as high as they were at this time last year.

Signs have been posted around the lake encouraging people to avoid illness by staying out of the water.

While avoiding lake water is voluntary and the lake and the areas around it are still open to the public, signs emphasize that contact with algae may cause symptoms ranging from nausea to seizures.

"The warning went up because the chlorophyll levels reached the threshold on all three locations that we test, which is required by the guidelines adopted by the Parks board," Mitchell Parks, Recreation and Forestry Director Nathan Powell said.

Chlorophyll levels in the lake are measured in parts per billion, and the threshold for a public health warning is met when readings are at or above 50 parts per billion in all testing locations. As of Friday, chlorophyll readings were 89 parts per billion at the center of the lake, 103 at Sandy Beach and 146 at Public Beach. Last year at this time, those readings were 24, 46 and 24, respectively.

Powell said boating and fishing in the lake are still safe, as they don't involve direct contact with the water, but that lake visitors should keep themselves and their pets out of the water.

Chlorophyll readings are done every Friday, and the warning will be lowered if chlorophyll levels in the coming weeks drop below the threshold.

The Lake Mitchell Advisory Committee will meet at 4 p.m. today in the Recreation Center's conference room to review Fyra Engineering's technical memorandum, which details possible strategies and related costs for solving the lake's algae problem.

The meeting will also include discussion of the proposed $8.86 million first step in cleaning up the lake in the long term. That step would be based on internal load control, or adding chemicals to keep the phosphorus at the bottom of the lake, and dam drawdown, which would regulate water levels in a way that would increase the amount of vegetation competing with algae for nutrients in the water.