Much of Lake Winnipesaukee is under a cyanobacteria bloom watch or warning heading into the busy Labor Day holiday. While state officials say people should still enjoy the long weekend, they should be careful about swimming near those collections of blue-green algae.
Cyanobacteria is a natural part of freshwater ecosystems. But under the right conditions, it can grow too much and cause harmful blooms. Those can produce toxins that are harmful to people, pets, and wildlife, causing symptoms that range from nausea and rashes to muscle paralysis.
Ted Diers, the head of the water division at New Hampshire’s Department of Environmental Services, says people should use good judgment when swimming or letting their pets swim.
“If you see an area that looks particularly gross, that has a lot of green stuff in the water, you know, you may not want to jump in the water right there,” he said.
Blooms can move quickly from area to area, and if parts of the water are clear, that probably means the concern for toxins is reduced, Diers said.
State officials have previously recommended against using water that’s had blooms for drinking, washing dishes, or bathing, even if it has been boiled or filtered.
The blooms on Lake Winnipesaukee right now are more widespread than the state has seen before, Diers said, calling them “somewhat historic.”
“Normally when we see cyanobacteria, it's on the shoreline,” he said. “What we're seeing is that it's in sort of those broad, windswept areas.”
Areas of Lake Winnipesaukee under watches or warnings include the waters off Alton, Tuftonboro, Wolfeboro, Governor’s Island, and The Broads. The lake had blooms earlier this summer, too.
Read more about how climate change is affecting cyanobacteria in New Hampshire and what you can do to prevent it.
The state’s healthy swimming mapper shows all active watches and warnings.
Warmer water temperatures and heavy rain can fuel more blooms, which are also influenced by the nutrients that flow into freshwater from human development nearby. The timing of ice on lakes can drive conditions, too, Diers said.
“This year there was practically no ice on the lake, so those conditions can set up sooner,” he said. “I think that that does not bode well for how this goes in the future, which means limiting the nutrient input is going to become more and more important.”
