by John Osborn ·
Friday, September 20, 2024
Swimming at the town beach remained off limits for people and pets this week as a late-summer algae bloom thickened and visibility remained unacceptably low.
The town’s sanitarian, Jim Garreffi of the Nashoba Associated Boards of Health, reported Tuesday morning that the concentration of cyanobacteria, commonly known as blue-green algae, had risen to 320,000 cells per milliliter, a 60% increase over the prior week’s 200,000 c/ml. The state requires that swimming be prohibited when the concentration of cyanobacteria exceeds 70,000 c/ml.
Visibility, as measured by the depth at which a black and white Secchi disk can be seen when lowered into the water, improved from 3 feet to 3.2 feet, but was still well below the 4 feet required by the state.
The two measurements mean that swimming at the beach is prohibited for people and pets. But the high levels of cyanobacteria and poor visibility are not limited to that area. Fishing and boating are allowed, but boaters are urged to steer clear of algae blooms and to thoroughly wash their boats at the water station near the beach entrance before departing to prevent the infection of other lakes and ponds.
The toxins released by cyanobacteria can cause skin or eye irritation. Inhaling water spray containing cyanobacteria can cause asthma-like symptoms and illness. Small children and pets are more susceptible to the effects of cyanotoxins than adults, and it can be fatal to dogs who swim in contaminated water.
But low visibility is also dangerous, Board of Health Chair Libby Levison reminded the Press in a brief interview Tuesday morning. “Even if this algae bloom were to stop but we still had only 30 inches of water visibility, we would not lift the swimming ban,” she said. “What if somebody goes to dive in and they can’t see a rock on the bottom? They could hit their head. It’s just too dangerous.” Camps don’t let children swim when visibility is less than 48 inches, she said. And if a swimmer goes under, high turbidity makes it difficult to locate the person.
While this week’s clear, sunny weather would traditionally have drawn sunbathers, swimmers, kayakers, and paddle boaters to the beach and pond, the area has been mostly abandoned since the ban went into effect. Every afternoon, however, scores of rowers, members of the Bromfield Acton-Boxborough rowing team, can be seen headed there for practice.
“We’re being mindful,” former program director Holly Hatton told the Press Monday afternoon, as team members assembled their shells and launched from the team’s beachside dock. The rowers hose down their boats after every practice, she said, and when a rower is splashed or falls into the water they are encouraged to rinse at the water station. Although the algae tends to collect in coves and near the beach, the entire lake is green, Hatton said, and thick weed growth makes parts of the pond impassable.
Hatton said the team was aware of the heightened threat in Harvard of mosquito-born Eastern equine encephalitis infection. The team provides insect repellent, though many members bring their own, and rowers return to shore and leave before dusk.
As long as the algae persists, Bare Hill Pond Watershed Management Committee Chair Bruce Leicher told the Press, plans for diver-assisted suction harvesting of weeds in the beach area (DASH) are on hold. The contractor is waiting to decide whether to return in October or next spring. He wrote: “I am not confident the algae will clear up in time for completing the project in October.” A benefit to waiting for spring, he said, is that the quantity of weeds to be removed will be less, allowing for more coverage of a larger area.
This year’s annual drawdown, however, will continue as planned. Town Administrator Dan Nason reported at Tuesday’s Select Board meeting that it will begin Oct. 1 and continue through the end of November, for a total drawdown of 6½ feet.