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For Immediate Release
October 7, 2021


Amanda McQuaid
(603) 848-8094 |

Cyanobacteria Bloom Sightings Update

The New Hampshire Department of Environmental Services (NHDES) is following up with several cyanobacteria bloom sightings that were reported this week. Please be on the lookout for cyanobacteria bloom accumulations, especially along the shorelines. Keep pets away from these accumulations. Blooms can appear in a variety of colors and are not always blue-green. Report your findings to NHDES, Harmful Algal Bloom Program at or (603) 848-8094.

Cyanobacteria Bloom Sightings:    green flecks of cyanobacteria in the water

•    Ayers Pond, Barrington
•    Beaver Pond, Derry
•    French Pond, Henniker
•    Long Pond, Pelham
•    Lower Suncook Lake, Barnstead
•    Millville Lake, Salem
•    Partridge Lake, Littleton
•    Province Lake, Effingham
•    Sunrise Lake, Middleton
•    Swains Lake, Barrington
•    Wilson Pond, Salem

Current Cyanobacteria Bloom Advisories
(ongoing advisories - sampled weekly):green cyanobacteria in the water

•    Arlington Mill Reservoir, Salem
•    Country Pond, Newton/Kingston
•    Harvey Lake, Northwood
•    Kingston Lake/Great Pond, Kingston
•    Northwood Lake, Northwood
•    Phillips Pond, Sandown
•    Pleasant Lake, Henniker
•    Silver Lake, Hollis

“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