For Immediate Release
Date: November 09, 2021


Amanda McQuaid
(603) 848-8094 |

State Warns of Late Season Cyanobacteria Blooms in New Hampshire

a cyanobacteria bloom with leaves in the waterCyanobacteria blooms have been observed along shorelines of a few lakes and ponds in New Hampshire this week. As the temperatures cool down, the water column begins to mix; a process also known as “Fall Turnover.” Nutrients may become available to organisms such as cyanobacteria which can help their growth. At the same time, cyanobacteria are reaching to the surface of the water for the warm sun. Cyanobacteria often accumulate along shorelines. Pet owners should be cautious nearshore where cyanobacteria may pile up.

There are two current and ongoing cyanobacteria advisories:
•    French Pond and Pleasant Pond of Henniker

Blooms have been observed at the following waterbodies:
•    Phillips Pond, Sandown
•    Province Lake, Effingham
•    Ossipee Lake, Broad Bay
•    Danforth Ponds, Freedom
•    Wheelwright Pond, Lee
•    Pine River Pond, Wakefield
•    Cobbetts Pond, Windham
•    Lake Kanasatka, Moultonborough
•    Lake Winnipesaukee, Greene’s Basin
•    Swains Lake, Barrington
•    Horace Lake, Weare

NHDES advises lake users and their pets to avoid contact with the water in areas experiencing elevated levels of cyanobacteria. 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. Please continue to monitor shorelines for changing conditions and avoid contact.

Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available in 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.

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