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New Hampshire Department of Environmental Services

Media Center

DATE: August 10, 2011
CONTACT: Sonya Carlson (603) 271-0698

Teresa Ptak (603) 271-8803

State Issues Cyanobacteria Lake Warning for Halfmoon Lake, Barnstead/Alton, NH

Concord, NH – An elevated cyanobacteria cell concentration has been measured at Halfmoon Lake in Barnstead/Alton, NH. Samples revealed that the state standard of 50% or greater of the total cells from the bloom were identified as cyanobacteria. As a result, the New Hampshire Department of Environmental Services (DES) has issued a cyanobacteria lake warning for those who recreate on Halfmoon Lake. The current bloom is variable with some lake portions free of elevated cell conditions while other areas have green clumps/flecks in the water. Recent sightings report elevated cell conditions at or near the center of the lake. Please continue to monitor your individual shoreline for changing conditions.

This warning is not based on a toxin evaluation and is intended as a precautionary measure for short term exposure. DES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions typically where lake water has a surface scum or blue-green flecks/clumps. DES also advises pet owners to keep their pets out of any waters that have a surface scum or blue-green or bright green flecks.

DES routinely monitors public beaches and public waters of the state for cyanobacteria. DES monitors public waters issued cyanobacteria warnings on a weekly basis until the cyanobacteria standards are again met. Cyanobacteria are natural components of water bodies worldwide, but blooms and surface scums may form when excess phosphorus is available to the water. Some cyanobacteria produce toxins that are stored within the cells but 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, nausea, vomiting, and diarrhea. Chronic effects include liver and central nervous system damage.

The August 10, 2011 warning will remain in effect until additional samples reveal cyanobacteria levels have diminished.

Photos and information about cyanobacteria can be found at the DES Beach Program web site:
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 DES immediately. Please call DES to report a cyanobacteria bloom at (603)419-9229.

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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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