Thanks to climate change, toxic bacterial blooms stick around for the fall

A sign indicates that Blanchard Beach at Oakledge in Burlington was closed on Friday. July 23, 2021, because of the presence of dangerous levels of cyanobacteria. File photo by Clare Cuddy

Toxic blue-green algae blooms have been a summer staple in some Vermont lakes for years. This year, the blooms are lingering through the fall.

Following widespread reports of blooms on Lake Champlain, the Vermont Department of Health on Monday warned Vermonters to remain cautious and look out for blooms, which often share an uncanny resemblance with pea soup. 

Blue-green algae blooms primarily plague Vermont’s waterways in the summer. However, due to climate change, warm water temperatures that are advantageous to cyanobacteria are increasingly likely to remain through fall, said Erin Eggleston, a biology professor at Middlebury College who specializes in microbes. 

The toxins that blue-green algae release can cause a wide range of health problems for people and animals — from rashes and diarrhea to liver failure and paralysis, according to the Centers for Disease Control and Prevention.

At times, cyanotoxins can even be fatal, the CDC says. Small children and animals who are more likely to ingest water while swimming are particularly vulnerable. 

Burlington Parks and Recreation staff consistently check for cyanobacteria blooms during the summer months, said Alec Kaeding, the beach manager for Burlington Parks and Recreation. Starting in mid-May, parks and recreation conducts visual checks at all of Burlington’s beaches at least twice a day and tests the water for cyanotoxins multiple times a week. 

But at this time of year, inspections are more sporadic. Seasonal staff generally retire after the summer, decreasing the department’s ability to monitor for blooms. 

“We ask that everybody keep an eye out,” Kaeding said. “Just be observant because we don't have the staff to check. But with all the people that come down to the beaches, if someone sees something and tells us, we’ll check it out.”

Cyanobacteria occur naturally in aquatic environments. They are one of the oldest species on earth and generally are harmless, according to the CDC. Cyanobacteria become dangerous when warm water and excess nutrients from fertilizer and septic waste cause them to multiply rapidly and turn into blooms. 

The blooms can transform portions of a lake like Champlain from crystal clear to a translucent, iridescent green overnight. When the cyanobacteria that form a bloom start to die, they release toxins.

Cyanobacteria thrive in warm water and are more likely to occur in water above 65 degrees, according to Bridget O’Brien, an environmental health scientist for the Vermont Department of Health. So as climate change increases air and water temperatures, it creates more favorable conditions for cyanobacteria. 

Lake Champlain warmed between two and seven degrees, depending on location, from 1964 to 2009, according to the state department of health. Lake Champlain hit 65 degrees this May, reached the high 70s in August, and didn’t dip back below 65 until October, the U.S. Geological Survey reported. 

Cyanobacteria blooms materialize all over the world. In the United States, the CDC says toxic blooms have been recorded in all 50 states, jeopardizing drinking water supplies, sickening people and animals and harming the economy.  

Cyanobacteria blooms occasionally have been recorded in Vermont as deep into the fall as late November, according to the state department of health. Central Vermont’s Lake Morey holds the record. A Nov. 27 bloom was documented there last year. 

Late-season blooms like that are generally created by different conditions than summer blooms, Middlebury College’s Eggleston said. 

In late fall, when leaf peeping season is long gone and frigid weather has just started to take hold, the cold air chills surface water, causing it to sink down and meet cooler water underneath. That mixes up the water and brings nutrients to the surface, triggering cyanobacteria blooms.

But Eggleston said this year’s early October blooms likely are related to the unseasonably warm weather.

“My hunch is that recent rains and warm, summer conditions are supporting the blooms, which indicates that conditions are more similar at this point in time to summer than we would think of for the fall,” she said. 

Scientists are still learning ways to mitigate the blooms. But Peter Isles, an aquatic biologist for the Vermont Department of Environmental Conservation, said one of the best things to do is reduce nutrient pollution in lakes and streams. 

That could mean adding vegetative buffers to agricultural areas, not spreading fertilizer before known rain events and building buffer zones around waterways, Isles said.

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Lana Cohen

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