A person who went crabbing in Chilmark Pond was sickened by what appears to be a neurotoxin from blue-green algae blooms in the water, according to Chilmark health officials.

At the Chilmark selectmen’s meeting Thursday evening, health agent Marina Lent told selectmen that a private citizen called her to say that a recreational crabber in the pond had “some pretty disturbing symptoms” that were consistent with blue-green algae blooms. The individual is currently recovering, officials said.

The town has put up signs at town landings and kayak haul-out points in both Chilmark and Squibnocket ponds, warning swimmers and other recreational pond users to be careful of the blooms. Ms. Lent said the blooms can be dangerous to humans, and that the danger is relative to the time and extent of exposure.

“The sort of immediate priority is to educate people that there is a high danger of ingestion,” Ms. Lent said. “In other words, swimming, or pets, or small children who don’t have any discipline about swallowing the water they are splashing around in, that is highly dangerous. Depending on the intensity of the bloom and the toxin, it is not advisable to have skin contact with the water at certain times.”

Although known as blue-green algae, the blooms are actually an amalgamation of toxic bacteria — called cyanobacteria — that thrive in warm, nutrient-rich waters. When conditions are right, the algae can form “blooms,” which then produce the toxins that can be dangerous to both humans and animals.

Symptoms from exposure to the toxins can include diarrhea, nausea, inflammation, breathing difficulties and other allergic reactions, according to the state Department of Public Health.

The blue-green blooms in Chilmark Pond, a closed, brackish Atlantic-facing pond that lies west of the Tisbury Great Pond, are relatively new. Last year, a dog in Chilmark died from ingesting water from the pond during an algae bloom, town administrator Tim Carroll said. He added that the individual reported on Thursday was the first adult to be poisoned by the blooms — which have occurred twice now this year.

“Just as a public awareness, people need to understand that dogs are at a great risk,” Mr. Carroll said. “And this year, we had our first human that was adversely impacted, by a significant amount. It was actually kind of frightening to hear his situation.”

Town officials did not share details of the individual’s symptoms or his name during the meeting.

But Mr. Carroll did report that a surfer noticed a bloom near Squibnocket Pond recently, prompting additional signage by the town landing.

According to Ms. Lent, it can be difficult to gauge the severity and dangerousness of the algal blooms. They often look different, and their color can belie toxicity — meaning that not all green-blue algae produce dangerous toxins. The challenge down the road would be determining when — and for how long — the ponds remained safe.

“This is a chronic issue,” Ms. Lent said. “There is no quick and easy way of saying yes, it’s safe here, and no, it’s not safe over there . . . We are working very hard on being able to assess it more closely, rather than, oh my god, it is green, we must address it.”

Ms. Lent also said that the regularity of the algal blooms was likely connected to climate change — and would be a problem for Chilmark in the future.

“We’ve really been digging into it with [water quality planner] Sheri Caseau with the MVC,” Ms. Lent said. “It is something that is an emerging issue that is likely connected to warmer weather and increased nutrients in the ponds. We did not used to have to deal with it. We will, going ahead, have this happen.”

In other business, selectmen agreed to auction off a four-acre town-owned parcel located off Meeting House Road. The property is at 4 North Ridge Road and is assessed at $642,100, according to land records. The property will have a minimum bid price of $695,000.

Bidding will open on Sept. 9 and close at two p.m. at Oct. 14, according to selectman Bill Rossi. Mr. Rossi said the moment had come to sell the parcel, considering the current real estate market on the Island.

“There’s not a lot available in town right now,” Mr. Rossi said. “And I think it is a really good time to sell a vacant lot in Chilmark.”

Selectmen also mulled instituting a service fee for residents to hook their residential fire alarm systems up to town public safety. According to an analysis by fire chief Jeremy Bradshaw, the town receives upwards of 200 fire alarm calls per year, costing the fire and police departments approximately $30,000 every year to respond.

He proposed a fee in the range of $200 to $300. Selectmen were receptive to the fee, although no action was taken.

Selectmen also discussed staffing at Squibnocket beach during public hours, noting that there had been large congregations at the beach after 5 p.m.

They also put off making a decision on whether tennis at the community center could continue past the school opening date of Sept. 17, but have approved play from the hours of 2 to 6 p.m. in the interim.

Selectman Jim Malkin gave a presentation summarizing the work of the town’s climate action committee. He noted that the Menemsha docks would likely be flooded every five and a half days during high tide, considering sea level rise, and predicted further erosion on the south shore, an increased risk of wildfire, and greater inundation of the town’s wetlands.

The committee suggested ensuring replacement for the Menemsha dock when the time comes, improving emergency planning and manning the fire tower 12 months per year, according to Mr. Malkin.

“We wanted to put a marker down, in terms of what we see, and what’s important for us to start moving on, rather than waiting on,” he said.