Sengekontacket Pond has been closed to shellfishing due to high levels of dangerous bacteria found in tests last week.
Water quality testing showed fecal coliform bacteria at levels well above the safe level for shellfish consumption at eight of nine testing stations on the pond. The contamination level at the ninth testing station was right on the upper limit of safety.
The samples were taken on June 5 and the pond was closed Friday, immediately after the results came back. It is likely to remain closed for another couple of weeks at a minimum while further tests are conducted and analyzed.
The closure does not affect boaters and swimmers.
Mike Syslo, senior marine fisheries biologist with the local office of the Massachusetts Division of Marine Fisheries, said while the readings were unusually high, they were not surprising, given a general deterioration in water quality in the pond over recent years.
"Frankly, for a lot of us who work on the pond, none of us are terrifically surprised at this," Mr. Syslo said.
"If you know the pond, there's a lot of birds on the perimeter and on the pond. Cormorants, seagulls, geese and other forms of ducks. This all contributes to that total count of fecal coliform.
"Our lab does not differentiate between human and animal. In the eyes of the federal and state public health institutions, they don't really care. A fecal is a fecal is a fecal.
"Either way it can make you sick."
Test readings were extremely high.
The maximum allowed level of fecal coliform is 28 bacterial colonies per 100 milliliters of water. Readings at eight stations in Sengekontacket Pond were greater than 51, the highest concentration the testing system registers.
"It doesn't get any higher than that," Mr. Syslo said. "We can't get a reading any greater. It could be 52, it could be 5,200, we don't know. Anything greater than 28 colonies is considered a violation."
The reading at the ninth station was 28.
Edgartown shellfish constable Paul Bagnall blamed the problem on recent weather conditions.
"We had extreme tides, we had a lot of rainfall, it's not really surprising that it was over," Mr. Bagnall said.
The shoreline and small islands in the pond were littered with large amounts of bird droppings that in some areas, like Sarson's Island, were several inches thick.
"So when you get the tide coming up, flooding more area, plus the rain sloshing out what isn't underwater, it's like taking a dump truck and dumping a load of manure in there," Mr. Bagnall said.
The paved surface of Beach Road added to the runoff problem.
While both Mr. Syslo and Mr. Bagnall said they were hopeful the pond would flush itself relatively quickly, they said the time is at hand when longer-term issues with Sengekontacket's water quality must be addressed.
"It would be nice - and we're talking about this now - to use some more sophisticated methods of sampling, that are quite expensive, but would ultimately allow us to differentiate between possible sources of the fecal coliforms," Mr. Syslo said, adding:
"It might be helpful to look at that to get a better plan of attack to clean the pond up, but I think most of us are convinced it's largely due to waterfowl. It's a shallow body of water, with a lot of waterfowl and not a lot of flushing. And the higher water temperatures as we move towards summer only cooks the process even faster, which is why you usually see the higher counts in the summer months."
Mr. Bagnall said he was cautiously optimistic about reopening much of the pond, but not all of it.
"We had been able to get some areas open through the winter," he said, adding: "Prior to this all of Trapp's Pond was closed and still is. An area right by the Bend in the Road, at Crab Creek, had been close, but we were able to get that area open. And there was an area that remained closed in Major's Cove. So when the pond's reopened I'm assuming those will remain closed."
Mr. Bagnall said the town had planned to open one area where shellfish stock had been reintroduced on July 1, but that's on hold now.
"Sengie was closed as a result of one test because it had high averages the previous three years. They get concerned when there's a number of stations off the chart," Mr. Bagnall said.
Although the closure would immediately affect only a couple of commercial quahaugers and probably several dozen people who like to family fish there, Mr. Bagnall said, the day could be coming when the pond was regularly closed for longer periods.
"It wouldn't surprise me if eventually Sengekontacket was open either only seasonally, or, as with a lot of towns off-Island, subject to rainfall closures. That is, if you receive a certain amount of rainfall within 24 hours, the pond is automatically closed for a period of say four to six days."
Mr. Bagnall said the pond would be tested again on June 18 or 19.
"And we'll see where we go from there," he said.