This summer, scientists are looking for a sometimes toxic organism that grows underwater in freshwater lakes, ponds and rivers to see if it’s prevalent in Lake Champlain.
Benthic cyanobacteria are ancient bacteria that grow in blobs on streambeds and lake floors. They rely on light and nutrients like phosphorus to grow, and there’s increasing evidence they can produce toxins that can kill dogs and make a person very sick.
Over the last decade, more people have been reporting these underwater blooms to the Lake Champlain Committee, says Lindsey Cookson, a scientist there who is leading the monitoring work alongside the engineering firm Tetra Tech.
Cookson says researchers are particularly concerned about a variety that grows in thick, underwater mats, which researchers elsewhere have found to be frequently toxic.
“They usually grow attached on the bottom, but when they grow tall enough, they will detach and float up to the surface,” Cookson said. “How do we inform people about them, has been the really big question that we're looking into.”
Cyanobacteria blooms are a growing water quality and public health concern in the United States. Until recently, most research and public health guidance has focused on the kind you can see on the water surface.
But researchers in Utah and the Great Lakes have tested mats of algae growing underwater and found toxins that affect the nervous system — or neurotoxins — in much higher concentrations in these submerged blobs than in surface blooms, which tend to produce other, less lethal compounds. Certain kinds of benthic cyanobacteria also appear to release neurotoxins more frequently than surface blooms.
Benthic cyanobacteria are diverse and can be hard to identify, says Hannah Bonner, a professor at Brigham Young University in Utah who studies benthic cyanobacteria.
Some are tan, black or blue-green, depending on the species and where it is in its life cycle. Some, she says, even look like little boba balls.
She and Cookson with the Lake Champlain Committee recommend people use something called “the stick test” to determine if a blob they encounter is harmless algae or benthic cyanobacteria.
“Picking up benthic cyanobacteria with a stick is like trying to pick up wet toilet paper with a stick. It's really, really difficult,” Cookson said.
If the substance is stringy, like fabric, Cookson says it’s most likely nontoxic filamentous green algae.
More research is needed to to understand when and why benthic cyanobacteria release toxic compounds, and what those compounds do in the human body. Sometimes, Bonner says, blooms can be harmless. Just how toxic a given submerged mat of bacteria might be is difficult to say.
“The good news about benthic cyanobacteria is that generally, dangerous concentrations of toxins are usually contained within the mat itself,” Bonner said. “Directly eating mat material is how you get exposed. Generally, those toxins are going to get diluted and disperse really quickly in the open water.”
Still, Cookson and Bonner recommend staying out of the water if you see what you think is benthic cyanobacteria, particularly at the surface.
Because so little is known about when these submerged colonies produce toxins and why, Cookson says the Lake Champlain Committee is studying the possibility that they could compromise the surrounding water quality.
The Lake Champlain Committee and Tetra Tech have funding to search for benthic cyanobacteria blooms in Lake Champlain for two years.
They hope to create a rubric for identifying different species of benthic cyanobacteria, and to determine which varieties growing here are most likely to be toxic.
Cookson says from what scientists know, the conditions that favor benthic cyanobacteria — warmer water, more nutrient runoff — are expected to happen more frequently as the climate changes.
She says Vermonters will need to learn to look for this environmental hazard.
The Lake Champlain Committee and Tetra Tech hope to publish findings about what kinds of benthic cyanobacteria are present here and what toxins they produce, along with more guidance for people recreating, next year.
