Slimy toxins cause concern at Silver Lake

HOLLIS – As New England goes through the deep end of a heat wave, swimmers are being cautioned about the potentially harmful cyanobacteria found in Silver Lake.

“It’s sort of swim at your own risk,” said Amanda McQuaid with the New Hampshire Department of Environmental Services.

Tests came back positive for cyanobacteria last week, and the greenish, hazy slime could be seen at the Silver Lake beach this week. According to a DES advisory, 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, tingling, numbness, nausea, vomiting, seizures and diarrhea. Chronic effects include liver and central nervous system damage.

Mark Le Doux, chairman of the Hollis selectboard, said concerns about the bacteria can be overblown.

“Most people don’t get sick from swimming in the cyano water,” Le Doux said.

Silver Lake has regular issues with cyanobacteria, Le Doux said, usually in the early part of the summer. The bacteria tend to die off as the summer progresses. The state is not keeping people from swimming at the Hollis beach, but instead has posted warning signs on the shore. Silver Lake is a state park.

Sandra Bridge, 32, of Nashua, brought her three young children to the beach this week. She spoke to park staff members about the signs, and headed to the water. Bridges said neither she nor her children have ever gotten sicks after swimming at the beach.

“We asked about it when we got here,” she said.

McQuaid said cyanobacteria is ubiquitous in New Hampshire’s waters, and is especially prevalent in shallow lakes and ponds. It can show up in small, shallow lakes where there are excess nutrients and warm water. That could indicate a problem with the lake’s watershed, she said.

Treating the cyanobacteria in the water is generally not optimal, she said. A popular quick fix is copper sulphate, and while that can kill off the cyanobacteria, it also releases more toxins into the system, she said. Some lakes and ponds are dredged or drained to deal with the cyanobacteria, but that does not get rid the organisms, she said.

In most cases, time will take care of the problem, she said.

“You actually just have to wait,” she said.

The warnings will remain posted until the bacteria dissipates. State officials will continue to monitor the lake, including conducting regular water tests.

Damien Fisher can be reached at 594-1245 or dfisher@nashua

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