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New Hampshire Department of Environmental Services

Media Center
DATE: July 17, 2013
Sonya Carlson (603) 271-0698 or (603) 419-9229

State Issues Cyanobacteria Warning for Horseshoe Pond, Merrimack, NH

Concord, NH - The New Hampshire Department of Environmental Services (DES) has issued a cyanobacteria lake warning for those who recreate on Horseshoe Pond, Merrimack, NH, due to extensive bluish-green clouds of cyanobacteria in the water. Samples collected throughout the pond were composed of Coelosphareium, Anabaena, Spirulina, Microcystis and Oscillatoria which are all capable of producing toxins harmful to humans and pets. Please continue to monitor your individual shoreline for changing conditions and avoid areas of contamination.

This warning is intended as a precautionary measure to prevent short term exposure to cyanobacteria toxins and is not based on a toxin evaluation. DES advises lake users to avoid contact with the water in areas experiencing a surface scum or blue-green clouds. DES also advises pet owners to keep their pets out of water that has a surface scum or blue-green clouds.

DES routinely monitors public beaches and public waters of the state for cyanobacteria. Once a cyanobacteria warning has been issued, DES returns to affected waterbodies on a weekly basis until the cyanobacteria bloom is not evident. 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 July 17, 2013, warning will remain in effect until additional samples reveal cyanobacteria levels have diminished. The lake will be re-inspected in 7 days to access conditions.

Visit the DES 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 DES immediately. Please call DES to report a cyanobacteria bloom at (603) 419-9229.

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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