MONTPELIER, Vt. — The 22 water systems in Vermont that draw from Lake Champlain are participating in a program to regularly monitor for a potentially toxic blue-green algae that shut down service to 400,000 customers in Ohio last summer.

While scientists say this summer is shaping up to be a bad one for blue-green algae on Lake Champlain, there have been a few reports of small amounts of the toxin detected in untreated water and none in treated drinking water, records show.

In previous years, the water system operators only sampled the water if an algae bloom was spotted near a water plant.

“I think a lot of people now, they’re scared, they’re thinking about it,” said Brian Bishop, the chief operator for the Swanton Village drinking water system that serves about 3,000 customers with water drawn from the northeastern arm of Lake Champlain not far from the most heavily affected Missisquoi Bay.

Bishop, who samples water from the village water plant on Lake Champlain’s Maquam Bay, said he and other public water officials have been following the threat posed by the potentially toxic blue-green algae blooms caused at least in part by phosphorous pollution flowing into the lake from rivers and streams.

Last summer officials who monitor drinking water taken from Lake Champlain paid close attention when the water system that draws water from Lake Erie for Toledo, Ohio, and parts of southeastern Michigan was overwhelmed by blue-green algae, leaving hundreds of thousands without safe tap water for two days.

Not all blue-green algae contains toxins, but people who come into contact with the toxins can get skin rashes, vomiting and diarrhea. The toxins have been known to kill dogs and other livestock.

“That really brought a lot of attention onto our blue-green algae program,” said Vermont state toxicologist Sarah Vose, who works for the health department. “A lot of people asked the question, could that happen here?”

Vose said the blooms on Lake Erie tend to appear earlier in the season than on Lake Champlain, where they tend to appear in early July, which is what is happening this season. Nevertheless, Vermont set up the testing program to check water both before and after treatment.

Mike Winslow, a staff scientist with the Lake Champlain Committee, which runs an algae monitoring program, said it’s shaping up to be a bad season for blue-green algae. Some beaches have been closed already this summer on both the Vermont and New York shores.

“It’s been rough so far,” said Winslow. “There have been a lot of blooms in a lot of places. They start, not unusually early, but early. It’s not a surprise given the rains that we had in June.”

Stormwater runoff can carry fertilizers from nearby farms into the lake, helping fuel algae blooms.

The results of the testing program, being paid for in part by two grants totaling $49,000 from the Centers for Disease Control and Prevention, are posted on the Vermont Department of Environmental Conservation website, Vose said.