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9/1/23 Cyanobacteria Update

The current advisory against water contact for people and pets in the Thomas Island area has been lifted by the City’s Health Department. The posters will be removed this afternoon. People can swim in and have contact with the water.

Laboratory testing of recent Planktothrix (the reddish cyanobacterium) bloom material did not detect any cyanobacteria toxins (anatoxins or microcystins).

However, it is important to know that the cyanobacteria could still pop up and should be avoided. “When in doubt, stay out.”

The City-sponsored routine cyanobacteria sampling is continuing with the assistance of LOPA volunteers. The City and LOPA appreciates all of the help with reporting on current conditions from the Thomas Island community.

If another bloom is observed, contact Jim McGrath as soon as possible at, or at 413-99-9344.

For more information on the health of Onota Lake, (or to become a member or volunteer), see the LOPA website at LOPA – Lake Onota Preservation Association (