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For Immediate Release
September 14, 2021


Amanda McQuaid
(603) 848-8094 |

State Warns of Several Cyanobacteria Blooms Observed in New Hampshire Waterbodies

harmful algal blooms seen on surface waterThe New Hampshire Department of Environmental Services (NHDES) is following up with several cyanobacteria bloom sightings that were reported today. There is a likelihood that cyanobacteria blooms are occurring elsewhere and are not limited to the following waterbodies. Always be on the lookout for blooms.

Cyanobacteria Blooms Reported on 9/14:

•    Arlington Mill Pond, Salem
•    Ayers Pond, Barrington
•    Big Island Pond, Atkinson/Derry
•    Contoocook Lake, Jaffrey
•    Country Pond, Newton/Kingston
•    Northwood Lake, Northwood
•    Swains Lake, Barrington

Current Cyanobacteria Bloom Advisories (ongoing advisories - sampled weekly):

•    Lake Kanasatka, Moultonborough. Issued 9/13
•    Silver Lake, Hollis. Issued 9/13
•    Kingston Lake/ Great Pond, Kingston. Issued 9/9
•    Harvey Lake, Northwood. Re-issued 9/7
•    Pleasant Lake, Henniker. Issued 8/26
•    Marsh Pond, New Durham. Issued 7/21

“Cyanobacteria Advisories” are issued when samples are collected and identified, with cell concentrations exceeding the state threshold of 70,000 cells/ml. “Cyanobacteria Alerts” are shared when photos and reports have been submitted to NHDES (and no samples have been collected or blooms have already dissipated). Advisories and alerts are not based on toxin evaluations and are intended as a precautionary measure. These messages are shared to inform the public to be on the lookout, and to be cautious in waterbodies with blooms.

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.  

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