Cyanobacteria Lake warning for Danforth Bay

A cyanobacteria bloom has been reported on Danforth Bay in Freedom, New Hampshire. Based on visual evidence reported August 15, the cyanobacteria bloom is accumulating along shorelines and coves, appearing as blue-green scums, flecks and patches. Others have described bright green clouds throughout the waterbody. A sample was collected August 16 to confirm identification and enumeration of the bloom. Cyanobacteria were identified as Oscillatoria and estimated to be > 1 million cells/ml. Cyanobacteria beach advisories and lake warnings are issued once blooms exceed 70,000 cells/ml. As a result, the New Hampshire Department of Environmental Services (NHDES) has issued a cyanobacteria lake warning for those who use the waterbody for recreation. The bloom can come and go quickly and tends to be patchy. It is advised to avoid contact with the bloom. Please continue to monitor your individual shoreline for changing conditions.

This warning is not based on a toxin evaluation and is intended as a precautionary measure for short term exposure. NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions typically where lake water has a surface scum, green streaks or blue-green flecks aggregating along the shore. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

NHDES routinely monitors public beaches and public waters of the state for cyanobacteria. Once a cyanobacteria lake warning or beach advisory has been issued, NHDES 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 scums may form when excess nutrients are available to the water. Some cyanobacteria produce toxins that are stored within the cells but released upon cell death. Toxins can cause both acute and chronic health effects that range in severity. Acute health effects include irritation of skin and mucous membranes, tingling, numbness, nausea, vomiting, seizures and diarrhea. Chronic effects include liver and central nervous system damage.

The warning went into effect on August 16, 2018, and will remain in effect until additional samples reveal cyanobacteria levels have diminished. NHDES will sample weekly to monitor the bloom on this waterbody.

Visit the NHDES Beach Program website for photos and more information about cyanobacteria at