Lambert’s Cove Beach, Seth’s Pond, Long Cove Pond and Tisbury Great Pond were all closed to swimming on Thursday after results from routine water testing revealed a spike in the bacteria enterococcus.

West Tisbury health agent John Powers said he expects the tests to be an anomaly and anticipated the beaches would be open again by today. He said the contamination at Lambert’s Cove may be in part due to a breach at James Pond.

The superintendent for The Trustees of Reservations, which manages Long Cove Pond and part of Tisbury Great Pond, was puzzled by the high readings.

“We’ve had several of these spikes in the past two years and we really can’t explain it,” said Chris Kennedy. “Usually if you have a lot of rain this can happen but we hadn’t had rain for five days before the readings. We’re kind of scratching our heads.

“It’s frustrating but all we can do is resample the water, hope this was an anomaly and just wait and see.”