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Toxic blue-green algae blooms are back in local ponds

A cyanobacteria bloom covers Walkers Pond in Brewster on June 25, 2020.
Gerald Beetham; Association To Preserve Cape Cod
A cyanobacteria bloom covers a pond in Brewster on June 25, 2020.

It’s summer on Cape Cod and that means toxic blue-green algae blooms are back in local ponds.

The algae is usually natural and harmless until it dominates an ecosystem and releases dangerous toxins, as has happened in Mashpee-Wakeby Pond on the Mashpee/Sandwich border and Long Pond in Barnstable. Those ponds are now closed to swimmers.

Andrew Gottlieb, with the Association to Preserve Cape Cod, says blooms are usually concentrated downwind, against the shoreline and people should keep an eye out.

"It's a surface layer of bright green, even fluorescent looking accumulation on top of the water. Throughout the remainder of the pond, it tends to be things that people often mistake as pollen," Gottlieb says.

He added that it’s particularly bad timing as hundreds of members of the Wampanoag tribe are expected to be home for the 101st annual powwow this weekend.

"You have people certainly coming in for the powwow and obviously Mashpee-Wakeby has significant ceremonial and emotional importance to the tribe. And so there's a certain added level of tragedy associated with this closure."

Human or animal exposure to toxic cyanobacteria can cause anything from skin irritation, to fevers, to major organ damage.

According to Gottlieb, the only way to keep our ponds safe, is to change human behavior.

"Until or unless we improve our wastewater treatment approach in homes near the ponds and people lay off the fertilizing and grooming of manicured lawns, we are going to continue to have green ponds."

Gottlieb says Cape towns need to build sewers and help people move away from backyard septic systems because they leak nutrients that act like fuel for the toxic blooms.

Eve Zuckoff covers the environment and human impacts of climate change for CAI.