State issues cyanobacteria warning for Silver Lake

Photo courtesy of the New Hampshire Division of Parks and Recreation Silver Lake State Park in Hollis

HOLLIS – The New Hampshire Department of Environmental Services on Tuesday issued a cyanobacteria warning for Silver Lake.

Water samples were found to contain the bacteria anabaena in excess of the state threshold, according to the warning that went into effect this week.

The freshwater bacteria, which is visible as blue-green clumps, is concentrated in specific portions of the lake with the highest concentration near the dam, according the DES warning.

While the warning is not based upon a toxin evaluation, DES advises lake users to avoid contact with those areas and for pet owners to keep their pets from them.

Dogs owners should especially take steps to avoid letting their pets drink the water, said Amanda McQuaid, DES public beach program coordinator.

DES routinely monitors public beaches and waters for cyanobacteria. Once a cyanobacteria warning has been issued for an area, DES tests it on a weekly basis until the levels are under the threshold.

Cyanobacteria occurs naturally in water bodies worldwide, but blooms and surface scums can form when excess phosphorus is introduced into the water. Some cyanobacteria produce toxins that are stored within the cells but released upon cell death.

Those toxins can cause short-term and recurring health problems that range in severity. Short-term health problems include irritation of skin and mucous membranes, nausea, vomiting and diarrhea, while long-term effects include liver and central nervous system damage.

Silver Lake, McQuaid said, has had high levels of cyanobacteria in the past, but that levels are currently higher than in recent years, likely due to rain mixed with recent high temperatures.

McQuaid said there are likely a number of factors that contribute to cyanobacteria growth in the lake, including that it is small, shallow and heavily used. Additionally, she said, there is significant amount of development and use of fertilizers around the lake, both which can cause phosphorous runoff.

She encouraged residents surrounding the lake to limit use of fertilizers that contain phosphorous.

On average, the New Hampshire DES issues cyanobacteria warnings for 10 to 15 blooms a year, McQuaid said.

Derek Edry can be reached at 594-1243, or @Telegraph_Derek.