Years ago, I enjoyed the opportunity to live on Pleasant Lake in New London, a beautiful hidden gem with clear water and views of Mount Kearsarge. I was sad to learn recently it had to be temporarily closed to swimming because of bacteria.
Anyone who knows the lake – deep, filled with fish and ringed by hills – would never associate its waters with bacteria. When I lived there, I not only spent hours swimming but also enjoyed the presence of loons (I’m glad to know they are still there!).
But as is happening on so many New Hampshire lakes in the past few years, a grim notice for Pleasant Lake went out: People and pets were told to temporarily stay out of the water because cyanobacteria blooms in three separate locations made swimming unsafe and exposure potentially dangerous.
Exposure to cyanobacteria – sometimes called blue-green algae – can cause liver damage; it is particularly dangerous to children and dogs, and in rare instances, it can be fatal. And while nutrient runoff from farms and septic systems is absolutely a major driver of the alarming increase in algae blooms on our lakes, the fuel for the increasing occurrences in New England freshwater ponds, lakes and streams is climate change.
State warnings and advisories about cyanobacteria have increased annually for the last five years. Some of the state’s most storied lakes and ponds have been affected, including Lake Winnipesaukee, which saw an historically high number of algae blooms last year. Other lakes with no history of blooms, like Pleasant Lake, are suddenly seeing them for the first time. The causes are clear and they are not going away.
New Hampshire’s winters have been warming for decades and now are about 4 degrees Fahrenheit warmer than in 1970. Virtually every year in the last decade was warmer than the prior year, with 2024 the warmest winter on record. That has had some obvious results: Less snowfall and a rapid diminishing of the time that ice stays on a lake, with impacts on ice thickness and how cold the water becomes. Lack of ice allows more sun to enter a lake, feeding algae and creating a warmer (better) growing environment.
In addition to affecting ice and causing warmer waters, climate change is also producing increasingly torrential rains. Tragically, this month has seen some of the worst flash flooding in the nation’s history with a terrible toll in lost lives. Rains are causing runoff into lakes across the state, carrying phosphorus from farm and lawn fertilizer and from septic overflows, which are all contributing to a perfect recipe for algae growth. Heavy rains in New Hampshire have led to flash flood warnings three times in the last five weeks alone.
Some steps are being taken on a lake-by-lake basis in New Hampshire, such as early detection of cyanobacteria blooms and physical removal of the blooms by a professional before they become dangerous, or chemical treatments to kill the blooms combined with efforts to block nutrient runoff from reaching the water. All are expensive.
A fund established in 2023 to help non-profit lake associations, communities and drinking water providers fight cyanobacteria, the Cyanobacteria Mitigation Fund, quickly ran out of money and has not been replenished.
We cherish our lakes, and this threat is not going away. As we bounce from heat wave to heat wave, punctuated with yet another bout of driving rain, we are only going to see more warnings for all of us, including our children and pets, to stay out of the water.
Lakes closed to swimming, heat waves in June, winters with no skating, driving rain and flash floods – they are all sending the same message: The root problem is our warming climate, and we need to do more to stop it.
Tom Irwin is Conservation Law Foundation’s Vice President for New Hampshire.