BARNSTEAD — The New Hampshire Department of Environmental Services has issued a cyanobacteria beach advisory for Halfmoon Lake in Barnstead, after finding an elevated concentration of the bacteria.

The bloom was observed on Aug. 16, appearing as green streaks in the water. The cyanobacteria were identified as Oscillatoria, estimated at 1.45 million cells/milliliter.

The warning is intended as a precautionary measure for short-term exposure. Lake users should avoid contact with the water in areas where lake water has a surface scum, green streaks or blue-green flecks aggregating along the shore. The department also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

Once a cyanobacteria lake warning or beach advisory has been issued, the state returns to affected waterbodies on a weekly basis until the cyanobacteria standards are again met.

Cyanobacteria are natural components of water bodies worldwide, but blooms and surface scum may form when excess nutrients are available. Some cyanobacteria produce toxins that are stored within the cells but released upon cell death. The toxins can cause both acute and chronic health effects that range in severity, from irritation of skin and mucous membranes, tingling, numbness, nausea, vomiting, seizures and diarrhea to liver and central nervous system damage.

The warning went into effect on Aug. 17, and will remain in effect until additional samples reveal cyanobacteria levels have diminished.

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