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New Hampshire Department of Environmental Services

Media Center

DATE: October 23, 2018
CONTACT: Amanda McQuaid (603) 271-0698 (O), 848-8094 (C)

State REMOVES Cyanobacteria Lake Warning for Showell Pond in Sandown, New Hampshire

Concord, NH – The New Hampshire Department of Environmental Services (NHDES) has REMOVED a cyanobacteria lake warning issued for Showell Pond on 8/8/2018. In this case, there was not a surface scum. The water appeared green, turbid and slightly cloudy throughout the water column. Samples were collected August 8, 2018 and cells were identified as primarily Anabaena/Dolichospermum; and a few colonies of Woronichinia were noted also. Cyanobacteria concentrations were elevated, estimated to be greater than 13 million cells/ml. The state threshold for a warning or advisory is 70,000 cells/ml of cyanobacteria in NH lake water. Weekly to bi-weekly sampling had been done since the advisory was first issued. On August 22, the cyanobacteria concentrations were elevated at over 1 million cells/ml. Each week, the estimates were over 1 million cells/ml. By September 6, the concentrations were estimated to be 9 million cells/ml. On October 3, estimates were 50 million cells/ml. Samples were not collected again until October 22, 2018. There was still a dominant population of Anabaena/Dolichospermum, however there were only about 2,000 cells/ml. Please continue to monitor your individual shoreline 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 August 8, 2018, and was removed on October 23, 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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