Sengekontacket Pond will be closed to shellfishing for four months each year in the peak summer season on a permanent basis, as a result of intractable problems with high levels of dangerous bacteria.
From now on the pond, which spans Edgartown and Oak Bluffs and is a popular spot for recreational clammers, will be closed from the start of April until the end of September annually.
The closure does not affect swimmers and boaters.
The decision was made last week by state fisheries officials and communicated to the town shellfish constables yesterday by Mike Syslo, senior marine fisheries biologist with the local office of the Massachusetts Division of Marine Fisheries.
The decision follows two closures in the past six weeks after tests revealed unsafe levels of fecal coliform bacteria. The new regime is expected to be in place for at least several years, pending the outcome of a planned major dredging program to improve water circulation and quality.
The first closure followed water sampling on June 5, which showed fecal coliform contamination well above the safe level at eight of nine testing points on the pond.
The maximum permissible level of fecal coliform is 28 bacterial colonies per 100 milliliters of water. Readings at eight stations were greater than 51, the highest concentration the testing system registers.
"It doesn't get any higher than that," Mr. Syslo said after the results came in. "We can't get a reading any greater."
The coliform count at the ninth testing point was 28.
It was initially hoped that the results were a short-term problem due to bad weather immediately preceding the testing.
"We had extreme tides, we had a lot of rainfall, it's not really surprising that it was over," Edgartown shellfish constable Paul Bagnall said.
The shoreline and isl ands in the pond were littered with large amounts of bird droppings - in some areas, like Sarson's Island, 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 pond was retested on June 19 and reopened despite results Mr. Syslo described as "borderline."
But on July 2 another series of nine samples again showed very high coliform counts - five at 50 or above, two at 36 and two at 28 - and the pond was closed again indefinitely, while Mr. Syslo and other experts considered what to do.
The high readings this time could not be blamed on rainfall; there had been almost no rain in the preceding two weeks. Furthermore the samples were taken not from shore, as they were previously, but from a boat in deeper water, which debunked the argument made by some that the sampling regime was to blame for the results.
All parties now agree that the source of the bacteria is waterfowl. High water temperatures encourage rapid multiplication of the bacteria and poor water circulation stops the pond from being flushed by the sea.
After the meeting yesterday, Mr. Bagnall said he thought the fisheries officers had taken the only decision they could under the circumstances, and he said the only real hope of rehabilitating the pond lies in a massive dredging program.
"There was some discussion of alternatives [to seasonal closure], but they had crunched their numbers pretty thoroughly," he said, "and it would have been a tough sell to argue for anything else. Bacteria levels have been creeping up in the summer months over the past four or five years.
"I'm hopeful that maybe by more aggressively dredging maybe we can get some areas reopened eventually."
But that could take several years and millions of dollars.
"Edgartown has a project underway for our side of the pond. We have [permitted] renewals probably 85 per cent done for what we've done there in the past, and we are moving toward getting a new permit which would allow dredging the big bridge back towards Trapp's Pond with another channel back to the Boulevard landing," Mr. Bagnall said.
"We've already done a lot of field work on it and next step with that is a meeting with the Massachusetts EPA [environmental protection agency]. We're looking at an environmental impact statement on it, but with that comes a bill for $100,000 to $200,000, just to get the permits.
"And then the project would probably be around a million bucks or more to do.
"The other renewal project is a bit less because it's not new and some of the previous channel still exists, but that will still be $700,000 to $800,000.
"I am an optimist and I am hoping we can start the project not this winter, but a year from then. It wouldn't surprise me, though, if it took a year beyond that. It's going to be fairly complex.
"The state owns the beach, the county manages it, technically the commonwealth of Massachusetts owns all the bottom of the pond, and the towns regulate the shellfishery."
Mr. Bagnall could not say where the money would come from to fund all the works other than: "If you want to do a dredging project on Martha's Vineyard, you've got to seek out some local funding, whether it's private or from the towns.
"In the meantime the Division of Marine Fisheries has assured us they will keep sampling the water, and we hope we can maybe shorten the closure a little bit. But that would probably only mean a week or two," Mr. Bagnall said.