The pond bottom and shoreline rocks below Rick Karney and Dave Grunden as they sit, discussing the reasons for this week's closure of Sengekontacket Pond to shellfishing, are green with weedy marine growth.
Nearby a duck, which has been feeding on the weed, raises its tail and drops another little contribution of fecal matter into the water. Right on cue, as if to underline the point that Mr. Grunden, the Oak Bluffs shellfish constable, has just made.
His point is that the increasing number of birds feeding and nesting on the pond are responsible for the bacterial contamination which forced state fisheries managers to decide, for the first time in Island history, to close Sengekontacket until the end of September. Sengekontacket will be closed to shellfishing for four months, from June through September the future.
The decision was an unfortunate one, for those who formerly enjoyed summer shellfishing, for the economies of Edgartown and Oak Bluffs, which share the pond and for the reputation of the Island as a pristine place. But it had to be made, given the declining water quality of the pond in the warmer months over recent years and two closures over the past six weeks, when testing showed fecal coliform counts far above the safe level.
The birds are the immediate cause of the problem; on that much all the experts - Mr. Grunden, and his counterpart in Edgartown, Paul Bagnall, and Mr. Karney, shellfish biologist and director for the Martha's Vineyard Shellfish Group, among others - agree.
But behind that are much harder questions. Why are there are so many birds and what to do about them? Why is the pond is not able to clean itself and what to do about that?
Could the bacterial problem be related to higher water temperatures as a result of climate change? Warmer water encourages bacterial reproduction. Could it be related to the other major water quality problem on the Island: higher nitrogen loads in the water as a result of human activity, which encourages the growth of algae and other marine weed?
There is plenty to speculate about, and, at the moment at least, not a lot of science to back any theory.
Mr. Grunden and Mr. Bagnall are pinning their hopes of rehabilitating the pond on dredging, to increase the rate at which Sengekontacket flushes into the sea. But they are frustrated by the slowness of the process of getting the various permits necessary.
Mr. Bagnall estimates it will take at least 18 months to obtain the necessary approvals, complete an environmental impact statement and begin the dredging itself. And possibly longer. Plus it will cost upwards of a million dollars.
But the water resource planner for the Martha's Vineyard Commission, Bill Wilcox, is not so sure. He suggests the pond flushes pretty well now, and says there is no guarantee dredging will greatly improve water quality.
"I've heard that in other areas where they've looked at dredging projects to improve the flushing of a pond, it was found to be only a small factor," he said, adding:
"In the case of Sengekontacket we just don't have the data to know whether dredging will help."
Like others, Mr. Wilcox is frustrated by the long delays in releasing the results of the Massachusetts Estuaries Project, a sophisticated scientific study on water quality in six of the Island's ponds, including Sengekontacket, which could provide the tools for better estimating the effects of dredging.
Mr. Grunden also acknowledged doubts.
"It's going to be very difficult to address the source of the bacterial contamination, so that forces us to treat the symptom as opposed to the cause," he said.
But you cannot just kill the birds, Mr. Grunden said. Most of the species are in some way protected, although he said there has been talk of disrupting the nesting of the cormorants.
"But," said Mr. Grunden, "even if it was legal I think it would be very difficult because the islands [in Sengekontacket] belong to Mass Audubon or Felix Neck. There would be controversy there."
Said Mr. Wilcox: "I was out on the pond the day after the last tests were taken that resulted in the closure. There were well over 100 Canada geese on Major's Cove and at least 200 cormorants on Sarsen's island.
Mr. Karney said: "It's almost unnatural the way the things have reproduced. You talk to some of the older fishermen, they don't remember cormorants."
The fact is, cormorants did not used to live here in significant numbers and Canada geese, once migratory, have become permanent residents. Habitat change must have something to do with it.
"The silent threat, the bigger threat I think, is the nitrogen input," said Mr. Karney, sitting on the dock on Lagoon Pond in front of the solar shellfish hatchery that he has managed for more than 20 years. "It may be aggravating the bacterial count. Watch the ducks along here. They're in here grazing on this algae. The more algae there is, the more ducks there are in here grazing on it."
As more weed grows, more of it washed up on shore, making increasingly thick wrack lines, Mr. Karney said.
"If you have a heavy wrack line because of heavy macrophyte growth, that will store bacteria and keep it alive longer. The light can't penetrate. Sunlight will kill a lot of bacteria," he said.
Mr. Wilcox, endorsing Mr. Karney's speculation, said he has seen studies suggesting bacteria could reproduce in the wrack.
And if further study shows a link between the nitrogen problem and the bacterial problem, other ponds could also be in trouble in the future.
Said Mr. Grunden: "It [nitrogen pollution] is in all the ponds. There really is no pristine water left on Martha's Vineyard. All of it is detrimentally impacted to some degree or other. So we've got our work cut out for us to slow or improve the direction things are going."
Other shellfishing areas on the Island remain safe at the moment, and Sengekontacket is still safe for swimming and boating.
But the future looks complex and difficult, particularly for Sengekontacket where previously, on a good day in summer, 100 or more people could be seen clamming.
There may be one small, silver lining for year-round residents, if not for summer visitors. In the fall, when some of the birds move on and the water temperature falls, along with the bacterial count, there is likely to be some very good shellfishing to be done on the pond.