Climate change is making cyanobacteria worse


New Hampshire Public Radio

Published: 06-22-2023 4:00 PM

As spring winds down and summer emerges, cyanobacteria season is also kicking into gear. While more people set foot into New Hampshire’s lakes and ponds, local environmental advocates are trying to find ways to mitigate and remove cyanobacterial blooms. That includes making sure people understand how their actions contribute to that growth.

Why should you care about cyanobacteria?

Cyanobacteria are photosynthetic microorganisms that can be found in all marine environments, including New Hampshire’s lakes.

Changes in weather trends — such as more severe yet infrequent rainstorms, as well as increasing temperatures — are allowing cyanobacteria populations to boom, said Kate Hastings, who manages cyanobacteria blooms with the New Hampshire Department of Environmental Services.

“When we have disturbances to the environment, cyanobacteria tend to be the ones that take advantage of that situation and grow out of control into these blooms,” Hastings said.

Cyanobacteria itself isn’t necessarily a concern, but when it reaches a certain density, it can release cyanotoxins.

“We can't really tell if a bloom is toxic just by looking at it. The wind can blow, then it accumulates somewhere else and it could magnify in concentration and therefore toxins,” said Amanda McQuaid, a state specialist in water quality and ecotoxicology.

Hastings said the state issued its earliest-ever cyanobacteria advisory this year — on May 16 — coupled with the most advisories issued in the month of May.

While the toxins cyanobacteria can produce are the greatest concern, McQuaid said, they’re also the hardest to understand. Some toxins can spur allergic reactions, including skin rashes. Others have the potential to cause nervous system failure or liver damage.

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In New Hampshire, if cyanobacteria cell density reaches 70,000 per ml of water, the state will issue an advisory to avoid that particular water body. State officials also recently launched a Healthy Swimming Mapper, which lists active alerts and advisories. These lakes won’t close down, but people are putting themselves at risk if they don’t heed the department’s advice.

Other factors such as urbanization have also been disturbing local lake ecosystems.

What can you do to decrease your contribution to blooms?

NH Lakes, a non-profit that works to preserve the health of lakes across the state, runs a LakeSmart program meant to show people how they can make a positive difference in the health of their lakes.

They offer a self-assessment survey to help people determine their potential role in cyanobacteria blooms. Homeowners can answer questions about how they manage their property, and what they do around or in the lake. Once submitted, it generates a personalized report of ways they are promoting the health of their lakes. It also gives recommendations on how they can manage their properties to preserve lake health.

“Homeowners are unwittingly introducing pollutants into the lake for these toxic bacteria to really grow and thrive,” said NH Lakes President Andrea LaMoreaux.

In June 2021, the Lake Kanasatka Watershed Association (or LKWA) completed a shoreline survey looking at 182 waterfront properties and found that 66% of the properties are likely having a negative impact on the lake. The survey was completed as part of their watershed management plan, which was published last August to identify pollutant sources and recommend ways to manage them.

While there aren’t any farms or golf courses around Lake Kanasatka, which are common bloom instigators, LKWA board member Lisa Hutchinson said homeowners introducing fertilizers, planting grass up to the shoreline and trimming away native plants can also cause blooms.

Cyanobacteria thrives off of nutrients such as phosphorus and nitrogen, which are commonly found in fertilizers.

During intense rainstorms, grass doesn’t absorb stormwater well, leading to runoff carrying these nutrients and other pollutants into the lakes. And if native plants are removed from the shoreline, this runoff has direct entry into the water.

“To some homeowners, it's easier to mow to the edge [of the lake] to see every little bit of that beautiful lake water,” Hutchinson said. “But the fact of the matter is it's not healthy for our lakes, and that's not what nature intended.”

What other steps are being taken to contain cyanobacteria? 

Last year, state legislators passed a law that directed the New Hampshire Department of Environmental Services to form a cyanobacteria advisory committee. The agency is scheduled to issue a statewide plan to potentially control and reduce cyanobacteria populations in November.

“There's several technologies out there now that potentially can remedy blooms, but many of them would require a permit here from the department,” said Dave Neils, who sits on the advisory committee and serves as chief aquatic biologist at the state environmental agency. “We just don't have a standardized rule set or law right now that allows us to do that. We're making do with what we have in a couple instances so far.”

State environmental officials used aluminum compounds, which bind to excess nutrients, to treat Nimpo Lake back in 2021, and they said they haven’t seen a cyanobacterial bloom there since. However, Neils said the planning and materials for that project cost about $200,000.

Ideally, Neils said, it’s best to avoid the blooms altogether, and getting rid of one is a last ditch effort. And that’s where advocates say people can be part of the solution.

“My advice is for people to not throw their hands up and say, ‘well, there's nothing I can do about toxic bacteria in my lake,’” said LaMoreaux, with NH Lakes. “Environmental problems [related to] climate change can seem really overwhelming.”

These articles are being shared by partners in The Granite State News Collaborative. For more information visit