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New Hampshire Department of Environmental Services

Media Center

DATE: September 21, 2018
CONTACT: Amanda McQuaid (603) 271-0698 (O), 848-8094 (C)

State REMOVES Cyanobacteria Lake Warning for Keyser Pond in Henniker, NH

Concord, NH –The New Hampshire Department of Environmental Services (DES) has REMOVED a cyanobacteria lake warning issued on 7/17/2018 for Keyser Pond. NHDES issues lake warnings for cyanobacteria when concentrations exceed 70,000 cells per milliliter of lake water. This waterbody has been carefully monitored by NHDES, the Henniker Conservation Committee and New England College researchers. Samples have been collected nearly every week to observe the conditions of the waterbody at two opposing shorelines and from the deep site of the lake. Samples were initially collected on 7/13 from the middle of the lake and cells were identified as Oscillatoria, Spirulina and Lyngbya at over 230,000 cells/ml (collected 5 meters below the surface of the water). Blooms were also observed along shorelines. Cyanobacteria concentrations were elevated on shorelines, ranging from 367,000 to about 4 million cells/ml on July 17. The bloom had primarily been comprised of Oscillatoria. However, there was a shift in species when samples were collected on July 26, revealing that there were also many fine filaments of Anabaena/Dolichospermum. Total cyanobacteria cell concentrations ranged from 135,000 to 6.5 million cells/ml along shorelines. On August 2, samples were collected from the three sites and cyanobacteria ranged from 100,000- 500,000 cells/ml. On both August 6 and August 10, samples contained cyanobacteria with concentrations estimated at nearly 500,000 cells/ml. on August 19, samples were collected but not enumerated. At that time, large clumps of Oscillatoria and Anabaena/Dolichospermum were surfacing in the millions. On August 25, samples were collected from the deep site (from a 5 meter depth) had concentrations of 500,000 cells/ml. On September 3, samples contained mostly Anabaena/Dolichospermum ranging from 81,000 cells/ml to 141,000 cells/ml along shorelines. Finally, on September 13 samples were collected from all three sites and it was revealed that the bloom had begun to dissipate. Viable cells of Oscillatoria and Anabaena/Dolichospermum remained, with concentrations ranging from 1,000 cells/ml to 25,000 cells/ml. Please continue to monitor your individual shorelines for changing conditions.

Cyanobacteria are natural components of water bodies worldwide, but blooms and surface scums may form when excess nutrients are available to the water. Some cyanobacteria produce toxins that are stored within the cells that can be 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 include liver and central nervous system damage.

NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions typically where lake water has a surface scum, green streaks or blue-green flecks aggregating along the shore. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

NHDES routinely monitors public beaches and public waters of the state for cyanobacteria. Once a cyanobacteria lake warning or beach advisory has been issued, NHDES returns to affected waterbodies on a weekly basis until the cyanobacteria standards are again met.

The warning went into effect on July 17, 2018, and was removed on September 21, 2018.

Visit the NHDES Beach Program website for photos and more information about cyanobacteria at
Updates on advisories and warnings may be obtained at
Follow the Beaches twitter feed:

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.

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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