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New Hampshire Department of Environmental Services

Media Center

DATE: August 30, 2018
CONTACT: Amanda McQuaid (603) 271-0698 (O), 848-8094 (C)

NHDES Cautions about Cyanobacteria

Concord, NH –These warm, final days of August are a great time to visit one of the thousands of lakes and ponds in New Hampshire. The water quality in our lakes is generally excellent. However, you should look before you leap in the water. The New Hampshire Department of Environmental Services (NHDES) is cautioning those who swim in and recreate around the state's lakes and ponds to be aware of cyanobacteria blooms. In particular, people and their pets should avoid contact with the tell-tale green blooms of cyanobacteria.

Over the past several weeks, the warm weather coupled with drenching rains and stormwater runoff (which carries excessive nutrients) have created conditions that are favorable for the growth of cyanobacteria.

Cyanobacteria can produce toxins that are harmful to humans, pets, and livestock. Toxins can cause acute health effects including irritation of skin and mucous membranes, nausea, vomiting, and diarrhea. In some cases, short term exposure can also result in nervous system interference including tingling, burning, or numbness sensations. Prolonged exposure can also lead to liver or kidney problems.

NHDES has issued dozens of cyanobacteria warnings this season. Updates to the list of lake warnings and advisories occur daily and are posted on the NHDES website (link below). It is likely that additional blooms are occurring or will occur in other waterbodies throughout the remainder of the summer and into the fall. Humans should curtail water contact while a bloom is ongoing. It is also important that pets and livestock not be allowed to bath or drink the water where blooms are present.

Cyanobacteria blooms are highly unpredictable in nature and can appear and disappear over the course of a day or, in some cases, last many weeks. In addition, bloom density will often shift based on wind direction such that higher densities occur on the side of the lake opposite from the prevailing wind. That said, most of the lakes in the state are perfectly clear of blooms. For these reasons, it is important to visually inspect the water every time a waterbody is visited. Cyanobacteria can appear as a green scum, or light green or blue flecks on the surface, or create a green hue to the water itself. Green streaks along the water's edge are also a good indicator of a cyanobacteria bloom. In short, if the water looks gross, don't swim in it!

While NHDES actively tests for these blooms, given their sometimes quickly forming nature, the public should still be diligent in avoiding waters with signs of cyanobacteria. Priority is being given to waterbodies that have the most severe blooms, and those that serve as public water supplies. Unfortunately, once a bloom occurs there is no immediate remedy to make it go away.

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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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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