The Martha’s Vineyard Land Bank will continue water testing in Ice House Pond this fall following a summer of off-and-on swimming closures due to high bacteria counts.

Land bank land manager Ian Peach said water sampling will extend into September as managers try to learn the source of the problem.

The pond was closed to swimmers three times this summer after testing above the state limit for enterococci, a bacteria that can cause infections.

Ice House in September. — Mark Alan Lovewell

The most recent closure was last week. The pond closed on Tuesday and reopened on Wednesday.

The source of the bacteria is unknown, Mr. Peach said, but he believes further testing is warranted.

“It could be a whole range of things,” he said, noting the erratic nature of many of the water sample results. The state limit for enterococci is 61 colonies per hundred milliliters. Mr. Peach noted that water sample results have seen a wide range. “To have such drastic swings where you see 200 [colonies] and then four the next day . . . I don’t see that much in former data,” he said.

The land bank sends water samples to the Wampanoag tribe laboratory in Aquinnah. Mr. Peach said he is exploring methods for more in-depth testing next summer.

“There’s potential to do samples where we can parse apart whether it was human or avian, for example,” he said. “It won’t answer all of the questions, but it gives us one more layer of understanding to plan for the future.”

The land bank has owned its property around Ice House Pond since 2003. Holdings at the Manaquayak Preserve were expanded in 2015 and now total 35.5 acres.

Information from the state Department of Public Health obtained by West Tisbury health agent Omar Johnson shows that the pond tested above the state limit for enterococci four times between 2015 and 2017.

Mr. Johnson said he has only been on the job for two summers, but has noticed an increase in bacteria levels from the water sampling test results.

“It looks like there was maybe more activity this year,” he said.

Nearby Seth’s Pond, a popular freshwater pond managed by the town, has seen no closures this summer due to bacteria levels.

Meanwhile, Ice House is now open to swimmers and water sampling will continue through the month. Usually testing is done for 12 weeks, from early June to Labor Day, Mr. Peach said

“We wanted to go a few weeks further,” he said.