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New Hampshire Department of Environmental Services

Media Center

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

State Issues Cyanobacteria Advisory for Elm Brook Park in Hopkinton, New Hampshire

Concord, NH – A cyanobacteria bloom has been observed along Elm Brook Park beach and shorelines around the reservoir in Hopkinton, NH.  Samples collected on 7/22/19 exceeded the State threshold of 70,000 cells/ml of cyanobacteria. Samples contained 258,000 cells/ml of the cyanobacteria taxa: Woronichinia, Anabaena/Dolichospermum, and Oscillatoria/Planktothrix. The bloom appeared as brown and orange streaks, with tufts of blue-green flecks. Surface blooms can rapidly change and accumulate in various locations around a waterbody. As a result, the New Hampshire Department of Environmental Services (NHDES) has issued a cyanobacteria advisory for those who use the waterbody for recreation. Please continue to monitor your individual shorelines for changing conditions and avoid contact. The beach is monitored by the Army Corp of Engineers (ACOE) and daily communication and observations will be made between NHDES and ACOE.

NHDES monitors public beaches and public waters of the state for cyanobacteria. Once a cyanobacteria advisory has been issued, NHDES returns to affected waterbodies weekly until the cyanobacteria standards are again met. NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

This advisory is not based on a toxin evaluation and is intended as a precautionary measure for short term exposure. Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available to 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. Be cautious of lake water that has a surface scum, changes colors, or appears to have green streaks or blue-green flecks aggregating along the shore. 

The cyanobacteria advisory went into effect on July 22, 2019 and will remain in effect until NHDES confirms that cell concentrations of the bloom have subsided.

Visit the NHDES Beach Program website for photos and more information about cyanobacteria at
Updates on advisories and warnings may be obtained at
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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.

The cyanobacteria bloom on Elm Brook on 7/22/19 appeared as brown and orange streaks, with tufts of blue-green flecks.

The cyanobacteria bloom on Elm Brook on 7/22/19 appeared as brown and orange streaks, with tufts of blue-green flecks


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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