Cyanobacteria Found In Two Harwich Ponds

 HARWICH – Two local ponds have been experiencing toxic cyanobacteria blooms in recent days. Public access to Seymour and Bucks ponds were posted as closed to protect the safety of people and pets.

 Conservation Administrator Amy Usowski said she was notified by Brewster Health Director Amy Von Hone on Sept. 18 that cyanobacteria was present on the Brewster side of Seymour Pond, but a visit to the public access to the pond off Route 124 in Harwich did not reveal signs of the toxic algae.

The pond was continually checked, and on Oct. 1, Usolski said, “pretty high concentrations” of dolichospermum, a toxic type of blue-green algae, was found on the Harwich side of the pond. Additional locations on the Brewster side of the pond also contained the algae.

Usowski said that on Oct. 4 she learned a blue-green algae was observed on the west end of Bucks Pond in the Great Sand Lakes section of town. The town posted a closure notice on public beachfront property and the Great Sand Lakes Association was notified to post its private beaches. 

Usowski said tests showed the presence of microcystis, a neurotoxin genus of cyanobacteria. Different types of toxins affect people and animals in different ways if they come in contact with them, said Usowski.

Two areas of Bucks Pond were checked because the town only has the authority to check public access locations on the pond. The neighborhood association members own most of the pondfront property.

“But we believe [the algae] was pretty much isolated to the west end of the pond,” said Usowski. “Hopefully these cool nights will help clean up these ponds.”

While temperatures have cooled, Usowski said she has seen people swimming in ponds, and people often walk dogs in the area.  She emphasized people should not swim in the ponds and dogs should not drink the water.

Notices posted at the ponds read: “Should you come into contact with the water, immediately shower with soap. If pets consume the water, immediately contact their veterinarian. The town of Harwich continues to monitor the situation and will remove this sign when the hazard  dissipates.” The signs will remain up until the hazard has abated, Usowski said.

The town is now required to report blooms to the Massachusetts Department of Public Health, which has a public notification program. Usowski also said she notified the Association to Preserve Cape Cod, which has a cyanobacteria pond monitoring program.

“We are starting to see more late season blooms,” Usowski said.   

“It’s not surprising to have cyanobacteria blooms during the fall months,” said Julie Hambrook, project director for pond and cyanobacteria monitoring programs at the Association to Preserve Cape Cod. “For several years there have been blooms that carried on for over a month.” 

 This year Santuit Pond in Mashpee began with high biomass and the “potential for concern” on Sept. 5, and Schoolhouse Pond in Brewster had a documented bloom on Sept. 9, both of which are still posted with public health advisories, said Hambrook.

 Cyanobacteria blooms are not easily predictable from year to year or season to season, with occasional spring blooms such as in Orleans this year, said Hambrook. Last year the bloom in Santuit began earlier in the summer, she said.

  Cooler temperatures in the fall are a complicating factor as the temperature throughout the pond equalizes, breaking the stratification that occurs during the summer months and causing turnover, with waters at different levels mixing and providing more nutrients to the plankton throughout the water column. This can stimulate fall blooms, according to Hambrook

This is the third cyanobacteria bloom in Harwich this year. Usowski said the bloom that occurred in the West Reservoir, just above the Herring River ladder in West Harwich, lasted more than a month. The reservoir was checked this fall and it looks fine, she said.

The blooms, according to Usowski, are caused by excessive nutrients, whether they come from the bottom of the pond or are entering through groundwater or other sources. There are a variety of ways nutrients can exacerbate the conditions, she said.