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New Hampshire Department of Environmental Services

Media Center

DATE: November 22, 2019
CONTACT: Amanda McQuaid (603) 271-0698 (O), 848-8094 (C)

State REMOVES Cyanobacteria Advisories for Three New Hampshire Ponds

Concord, NH - NHDES has removed cyanobacteria advisories for Showell Pond in Sandown, Hopkins/Adder Pond in Andover, and Perham Corner Pond in Lyndeborough this week. All three waterbodies had elevated levels of Anabaena/Dolichospermum for several weeks. Samples collected this week revealed cyanobacteria presence but at low levels, well below 70,000 cells/ml (state threshold for issuing cyanobacteria advisories).

Advisory dates:

  • Showell Pond, Sandown: 8/20 – 11/18
  • Hopkins/Adder Pond, Andover: 10/11 – 11/21
  • Perham Corner Pond (aka Morison's Pond), Lyndeborough: 8/20 – 11/21

Cyanobacteria are natural components of waterbodies 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.

There are no current cyanobacteria advisories in the state at this time and the monitoring season will resume in spring 2020. Please contact Amanda McQuaid with any questions or concerns about cyanobacteria blooms in New Hampshire.

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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