For the first time in five years, parts of Sengekontacket Pond will be open for shellfishing, at least through June. In July, August and Sepetmber the current plan calls for possible closures following periods of heavy rainfall, but otherwise the same parts of the pond now designated as safe for shellfishing will be kept open.

“Finally some good news,” Edgartown shellfish constable Paul Bagnall told the town selectmen at their meeting Monday, when he announced that parts of Sengekontacket from below Sarson’s island to an area near the Little Bridge have been declared open for shellfishing by state environmental officials from May 1 through June 30. The opened areas of the pond will be subject to possible closure at times from July through October depending on rainfall amounts, shellfish constables said in Oak Bluffs and Edgartown.

Other parts of the pond, including Major’s Cove and the Cow Bay end of the pond, remain closed to shellfishing.

The closures do not apply to boaters or swimmers.

Since 2007, Sengekontacket has been closed to shellfishing by the state from the start of summer through early fall because of high levels of fecal coliform bacteria in the water. The source of the bacteria has been the subject of widespread community discussion, speculation and study but is still not known precisely. Waterfowl are believed to be a significant contributing factor. A large population of water birds, including cormorants, congregate around Sarson’s Island, a small island in the center of the pond.

The large pond which spans the towns of Oak Bluffs and Edgartown is bordered by Beach Road on the Nantucket Sound side, while on the land side it is bordered by residential housing and the Felix Neck Wildlife Sanctuary. Extensive testing has been under way for years in Sengekontacket. Among other things the tests show that bacteria levels in the pond spike following periods of heavy rainfall. The state-mandated closures have frustrated town leaders and shellfish managers who have worked diligently to get to the root of the problem.

Along with his counterpart in Edgartown, Oak Bluffs shellfish constable David Grunden said the openings in the pond come as good news. A memorandum of understanding among Edgartown, Oak Bluffs and the state Division of Marine Fisheries has been signed by the state and is expected to be signed by the two towns, allowing the ponds to be opened for most of the summer, Mr. Grunden confirmed.

The decision to open the pond is due to lower bacteria levels, he said. “The Division of Marine Fisheries decides solely on their bacteria samples and analysis,” he said.

Once the memorandum is signed, the pond will be subject to rain closure rules from July through October, with July being the most restrictive month, Mr. Grunden said. If the area receives more than .2 inches of rain in a 24-hour period, the pond will be closed for a minimum of five days. From August through October, the level will be bumped up to one inch.

In some areas of the pond, shellfishing is prohibited at all times of year, while in others the closure is subject to conditions.

The state will check rainfall levels at 7 a.m. daily, Mr. Grunden said.

As a result, the schedule of when areas will be open or closed will change from month to month, which may cause some confusion, Mr. Grunden said. Each town will use flagpoles to indicate pond conditions; in Oak Bluffs, the pole will be near Little Bridge. When a red flag is flying, the pond is closed to shellfishing. In Edgartown, the flag will be located by the big bridge, clearly visible from the road and the pond, said deputy shellfish constable Warren Gaines.

Information about closures will be available by calling the Edgartown shellfish department at 508-627-6175 or by checking the town Web site which is updated frequently.

“We’re hoping for a dry July,” Mr. Grunden concluded.

“It’s great if it goes through,” he added, although “it’ll be a lot of getting used to and explaining to people what’s open and what isn’t.”