BOSTON (AP) – Boaters off the coast of Massachusetts have discovered three endangered giant sea turtles since Thursday entangled in buoy lines and struggling to survive, New England Aquarium officials said Sunday.

The massive turtles, weighing on average about 1,000 pounds, are summer visitors to the region.

The three turtles were found entangled on Thursday, Friday and Saturday.

“To have three in three days is very unusual,” Aquarium spokesman Tony LaCasse said. “It’s a problem up and down the coast.”

Two of the three turtles were freed. A fisherman Thursday in Provincetown Harbor freed one by cutting a buoy line.

On Friday, fishermen maneuvered a buoy to free a turtle on the Cohasset coast.

Sailboaters in Nantucket Sound on Saturday discovered another entangled turtle, but its status is unknown. One boater jumped into the water, which officials said is extremely dangerous.

LaCasse said boaters who see leatherbacks caught in lines should call the Coast Guard and stay with the animal if possible to give rescuers a precise location.

The turtles are likely to dive underwater for long periods of time, he said, and can stay under for up to an hour.

Leatherback sea turtles, the largest living turtles, are listed as an endangered species by the federal government.