“What is blue-green algae?”Officials unpack Lake Champlain’s perennial pest

A Cyanobacteria bloom forming on Lake Champlain. Photo courtesy of VT. Dept. of Health.

By Michael Frett
Islander Correspondent
GRAND ISLE – Every summer it closes beaches, sours the air with a putrid odor and colors Lake Champlain’s shores with a sickly green.
Scientists call it cyanobacteria, though most Vermonters seem to have settled with the more easily understood “blue-green algae,” and it is an almost guaranteed summertime guest during any given Vermont summer.
But what is “cyanobacteria?”
That was the question state researchers hoped to help Vermonters answer last week during a remote forum on Lake Champlain’s perennial pest.
At the most basic level, cyanobacteria are small, single cell organisms that feed through photosynthesis, the process in which plants use energy from sunlight to convert carbon dioxide and water into oxygen.
“They’re actually the first organisms on the planet that developed photosynthesis,” Peter Isles, an ecologist with Vermont’s Dept. of Environmental Conservation, said, “and as such, we can thank them for things like having oxygen we can breathe.”
According to Isles, cyanobacteria are fairly common organisms living in “almost every environment on Earth” and are a “natural and important part of most ecosystems.”
“I say this because it’s not always a cause for concern if there’s a little bit of cyanobacteria present in your lake,” Isles said. “There are cyanobacteria present in every lake.”
Where cyanobacteria become a problem, however, is when they clump together into the thick colonies people have dubbed “blooms,” where they take on the greenish hues that inspired cyanobacteria’s more commonly known name “blue-green algae.”
According to Isles, Vermont has five known varieties of problematic cyanobacteria, each taking on their own alien shapes when peeked at beneath a microscope and each one capable of forming the occasionally toxic blooms of “blue-green algae” stifling Vermont’s waterways.
Relative to other major bodies of water like Lake Erie or China’s Taihu Lake, Lake Champlain’s annual cyanobacteria blooms are rarely as overwhelming, though some corners of Lake Champlain, like the beleaguered Missisquoi Bay, will regularly see more severe blooms between summer and fall.
When blooms are severe enough, according to Isles, they can extract a toll on their local environments, depleting the amount of oxygen available within a lake and resulting in what scientists call a “fish kill,” the localized dying-off of fish populations.
Cyanobacteria can also sometimes be toxic, prompting the beach closures and drinking water concerns that tend to accompany late summer months in Vermont.
According to state toxicologist Sarah Vose, scientists do not currently know when a cyanobacteria bloom becomes toxic or what prompts cyanobacteria to begin producing toxins. It is for this reason public health officials opt for beach closures immediately after a bloom appears.
“We never really know when a bloom is producing toxins, and that’s something scientists are still trying to understand,” Vose said. “Even when they have the genetic capability to produce toxins, sometimes they do and sometimes they don’t.”
What scientists do know, however, is that when cyanobacteria do produce toxins, those toxins can be dangerous.
The deaths of several dogs in Vermont have been connected to cyanobacteria blooms. A severe bloom in Utah several years ago prompted more than 100 calls to the state’s poison control agency. Exposure to a bloom in Uruguay led to a child’s liver, the organ most affected by cyanobacteria poisoning, failing.
After a toxic bloom of blue-green algae in Lake Erie prompted the Ohio city of Toledo to temporarily shut off a supply of tap water for more than 400,000 residents in 2014, Vermont began providing for weekly tests of its own freshwater sources for drinking water.
According to Vose, there have been no known reports of drinking water in Vermont being found toxic since 2015.
While the primary source of poisoning from blue-green algae blooms stems from accidentally drinking or breathing in infested waters, public health officials also advise against boating over cyanobacteria blooms due to the possible threat of cyanobacteria being kicked into the air by boat and jet ski engines.
Officials also ask locals to avoid brining pets or children near infested shorelines and ask Vermonters to report cyanobacteria sightings to beach managers and the state’s health department.
How to address Vermont’s blooms of cyanobacteria is another question state officials hoped to help answer with last week’s meeting.
According to Isles, cyanobacteria need several ingredients to sustain themselves within Vermont’s waterways. Two of those, carbon and sunlight, Vermonters have no control over. The other two, however, have become the targets of multi-million-dollar efforts to improve water quality in Vermont.
“The things humans really control are nitrogen and phosphorus,” Isles said, “in particular phosphorus.”
In recent decades, Vermont’s watersheds have been carved by state and federal officials into a number of tactical basin plans and total-maximum daily load agreements intended to stymie nitrogen and phosphorus flow into Vermont’s rivers and lakes.
With the notable exception of Vermont’s east, where those documents target nitrogen flowing through the Connecticut River, most of the state’s water quality targets relate to phosphorus, an important nutrient for plant growth often found in fertilizers and other practical chemicals.
Since 2016, Vermont has invested more than $194 million through contracts and grants to address nutrient pollution in Vermont’s waterways, according to the state’s most recent Clean Water Initiative performance report.
Those funds have targeted everything from wastewater treatment plants to the implementation of farming practices intended to slow phosphorus runoff from fertilizers, to the installation of an expensive aeration system in Franklin’s Lake Carmi, currently Vermont’s only official “lake in crisis.”
As of the 2018 State of the Lake report, a publication updated every three years by the federally funded Lake Champlain Basin Program, Vermont had reduced the amount of phosphorus washed annually into Lake Champlain’s watershed by about 13% of what is mandated under federal orders.
Those numbers are expected to be updated with the release of the 2021 State of the Lake report later this week.
According to Isles, while the effects of a warming climate have led some to fear cyanobacteria blooms will become more severe and more common, research also suggests managing the flow of nutrient runoff into watersheds will have a more direct impact on the prevalence of blue-green algae blooms.
“This means we have the potential to control blooms even if warming continues by managing nutrients now,” Isles said.

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