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For Immediate Release
November 6, 2020


Amanda McQuaid, Harmful Algal Blooms Coordinator
(603) 271-0698 |

State REMOVES Cyanobacteria Advisory for Harvey Lake in Northwood, NH

Concord, NH – The New Hampshire Department of Environmental Services (NHDES) has removed a cyanobacteria advisory for Harvey Lake. Samples have been collected weekly since the start of the advisory (September 9). Cell concentrations were elevated above the 70,000 cells/ml state threshold, until this week when samples revealed that cyanobacteria had finally lowered to 1,500 cells/ml. Please continue to monitor your individual shoreline for changing conditions. Avoid swimming in areas that appear green, turbid, and/or creating a surface scum.

NHDES monitors public beaches and public waters of the state for cyanobacteria. Once a cyanobacteria advisory has been issued, NHDES returns to affected waterbodies weekly until the cyanobacteria standards are again met. NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

This advisory was not based on a toxin evaluation and was intended as a precautionary measure for short term exposure. Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available to the water.  Some cyanobacteria produce toxins that are stored within the cells and 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 may include liver and central nervous system damage. Be cautious of lake water that has a surface scum, changes colors, or appears to have green streaks or blue-green flecks aggregating along the shore.  

The advisory went into effect on September 9 and was removed on November 6, 2020. However, lake-goers should be on alert if they experience areas of the lake with surface scums.

If you notice anything resembling cyanobacteria, please refrain from wading, swimming or drinking the water. Keep all pets out of the water and contact NHDES immediately. Please call NHDES to report a cyanobacteria bloom at (603) 848-8094 or email