Following two weeks of consistently recording cyanobacteria at levels below a state health advisory, the Town of Mashpee Department of Natural Resources and Health Department have lifted the health advisory for recreating in Santuit Pond.
Signs warning the public against swimming and ingesting the water came down over the weekend.
“The Santuit bloom is subsiding,” director of natural resources Richard H. York Jr. said.
Cyanobacteria can produce harmful toxins, even release aerosol, which, when ingested or inhaled, can lead to liver damage. It can also degrade the vitality of a pond, leading to fish kills.
In mid-June, Mr. York found a level of 76,533 cyanobacteria cells per milliliter of water. The state threshold for posting advisories is 70,000 cells/ml.
The town installed the signs in June after a reading above the state’s threshold for a health advisory, warning the public not to swim in the water and especially not to drink the water. The advisory also cautioned against allowing pets in the area that might drink the pond water.
On July 3 Mr. York found the levels had gone down below 70,000 cells/mi, the state minimum, for the first time this summer. The state advises that a level below the threshold be maintained for two weeks before reopening a pond for recreation.
On Tuesday, July 16, Mr. York said that readings had dropped below 10,000 cells/mi.
Additionally, a seventh SolarBee, a water mixing device that circulates nutrients in the pond and provides oxygen, was installed. For Mr. York, that meant that hopefully the toxin will not return. The company that provided the six SolarBees provided the seventh for free for two years, after which the town can purchase it.
While Mr. York said that the town has no restrictions on the water, he cautioned against drinking it.
Mashpee Health Agent Glen E. Harrington said that it was okay to swim in the pond. None of the concentrated mat of algae was present in the swimming area of the pond at the time the advisory was lifted, Mr. Harrington said. The health agent also said that the advisory suggested that people swimming take a shower after doing so.
While the town has given the green light to recreate at the pond, others in the science community are cautious about preemptively lifting the ban.
Bryan Horsley, a restoration technician with the Association to Preserve Cape Cod, said that the association sampled Santuit water on July 9 and found that the bloom was still active. The association, a Cape-based environmental watchdog, has been sampling freshwater ponds throughout the Cape, and specifically for cyanobacteria.
Mr. Horsley noted that levels had dropped since the first reading of cyanobacteria in June, but there was a bright green surface on the pond when he visited last week. During a July 13 reading, following the lifting of the advisory, Mr. Horsley found that levels had come down, and that the pond was even clear.
But he noted that it had not been two weeks since his earlier July reading. The state advises a two-week period because when cyanobacteria levels decrease their volume in the pond, the bacteria is breaking down and potentially releasing toxins into the the pond’s water.
Mr. Horsley does not doubt the town’s sampling. But the difference in readings was based on how the two agencies sampled for cyanobacteria. Mr. York and the Town of Mashpee sample water further out into the pond. Mr. York is following state protocol for measuring the toxins. APCC and Mr. Horsley sample water near the edge of the pond as well as the scum buildups on the pond’s surface, which is essentially a concentrate of algae and cyanobacteria.
Regardless, both agree that the levels of the bacteria have been dropping in the pond.