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For Immediate Release
September 25, 2020


Amanda McQuaid , Harmful Algal Blooms Coordinator
(603) 848-8094 |

Update on Cyanobacteria Advisory for Spofford Lake in Chesterfield, New Hampshire

Concord, NH- A cyanobacteria bloom has been observed on Spofford Lake, appearing as black mats along some of the shorelines. The mats of cyanobacteria have come from the bottom of the lake and are washing along the shores, carried by winds and currents. The type of cyanobacteria was thought to be Lyngbya (speculatively Lyngbya wollei due to its morphological characteristics and black appearance). However, Green Water Laboratories have identified it as Stigonema, Scytonema and Tolypothrix. They also found that there were non-detectable levels of two toxins produced by the cyanobacteria (microcystins and saxitoxins). The identification of these mats will still be further genetically analyzed through a collaboration with Keene State and NHDES. These taxa, collectively, can produce an array of toxins not tested. These mats can cause rashes and NHDES still advises that lake goers avoid contact with these mats of cyanobacteria. The advisory is not based on a toxin evaluation and is intended as a precautionary measure for short-term exposure.

Surface blooms can rapidly change and accumulate in various locations around a waterbody. Please continue to monitor your individual shorelines for changing conditions. NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions, also known as a bloom. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

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 cyanobacteria advisory went into effect on September 10, 2020, and will remain in effect until NHDES confirms that bloom has subsided.
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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