skip navigation
New Hampshire Department of Environmental Services

Media Center

DATE: August 9, 2018
CONTACT: Amanda McQuaid (603) 271-0698 (O), 848-8094 (C)

State REMOVES Cyanobacteria Warning for Weirs Channel in Laconia, NH

Concord, NH – The New Hampshire Department of Environmental Services (DES) has REMOVED a cyanobacteria warning issued on 6/29/2018. The advisory was issued based on visual evidence of accumulations of cyanobacteria along the channel. Cyanobacteria were identified as Anabaena/Dolichospermum, Microcystis, and Woronichnia with the cell concentrations in the millions. Samples were collected along the channel on July 3 and July 18 with cyanobacteria still present. Samples were also collected towards the Weirs Beach location and from Paugus Bay, at the 2 ends of the channel on these dates. Some cyanobacteria were identified near the beach but in low concentrations. No cyanobacteria were observed in Paugus Bay. There have been no further reports of the bloom and it likely dissipated in mid-July. Samples collected August 8, 2018 showed only one colony of Microcystis. Please continue to monitor your individual shorelines 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 June 29, 2018, and was removed on August 9, 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

copyright 2017. State of New Hampshire