State Issues Cyanobacteria Advisory for Forest Lake in Whitefield & Dalton, New Hampshire

Concord, NH - A cyanobacterial bloom has been observed at Forest Lake in Whitefield and Dalton, NH. Samples collected on 7/18, 7/19 and 7/20 exceeded the state threshold of 70,000 cells/ml of cyanobacteria in lake water. The water contained at least 1 million cells/ml of Anabaena (Dolichospermum) from samples collected on July 18. Samples also contained Microcystis and Aphanizomenon. Though it appears that the bloom has dissipated, samples collected on July 20 contained 225,000 cells/ml. As a result, the New Hampshire Department of Environmental Services (NHDES) has issued a cyanobacteria advisory for those who use the waterbody for recreation. The advisory is not based on a toxin evaluation and is intended as a precautionary measure for short term exposure. Lake-goers should continue to be on the lookout for blooms and avoid contact.

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 July 20, 2020 and will remain in effect until NHDES confirms that cell concentrations of the bloom have subsided.