Chilmark town beaches Lucy Vincent and Squibnocket remain closed to swimming after droves of Portuguese man-of-war began washing up on the southern shore of the Island Monday, stinging five swimmers within minutes at Lucy Vincent. Two of the swimmers were hospitalized and released for wounds from the jellyfish-like creatures.

"Right after that happened, we decided to close swimming," assistant supervisor to Chilmark beaches Karyn Pietruska said. "Every morning since then, we've gone out to see how many there are."

Ms. Pietruska said the beaches will remain closed to swimming until the man-of-war, with their distinctive blue bubbles and their stinging tentacles, are no longer washing up. An offshore breeze will be necessary to push the creatures away, she said.

There were also riptide and high surf advisories this week from the National Weather Service, with the highest risk on the south coast beaches. The warning was in effect until 9 p.m. last night.

The quantity of man-of-war washing up on beaches - at a time when the ocean water is still quite cold - is unprecedented, according to veteran authorities on the south-facing beaches.

Ms. Pietruska reported finding 25 of the stinging creatures on Lucy Vincent beach and 12 on Squibnocket on Monday. On Tuesday there were 35 on Lucy Vincent and 13 on Squibnocket, and on Wednesday there were 15 on Lucy Vincent and five on Squibnocket. At press time yesterday, 18 man-of-war had been found on Lucy Vincent and 15 at Squibnocket. Surfers reported seeing at least eight more floating in the water off Squibnocket.

The man-of-war ranged in size from very small, about the size of an egg, to about eight inches long, Ms. Pietruska said. Although they are commonly thought of as jellyfish, Portuguese man-of-war are actually siphonophores, a colony of four sorts of polyps.

The creatures are also washing up in smaller numbers on Long Point beach in Chilmark, South Beach in Edgartown and on Chappaquiddick along the southern shore and out to Wasque. No sting injuries have been reported on any of the beaches so far, so there has been no reason to close them to swimming.

"We're certainly seeing a fair amount of them," said Christopher Egan, manager of Long Point beach, owned by The Trustees of Reservations. "To have these numbers is not something we've seen before."

Man-of-war, which cannot swim, move along with currents or wind that pushes the air bladder, known as a sail, along the water's surface. It is unclear why so many have entered the Island's cold waters and how long they will be here.

"We did have the tropical storm that passed by us. I'm not sure if this was because of that. It's hard to say," Mr. Egan said. "It could be that the Gulf Stream is running closer to the Island right now. These are just guesses," he added.

Both Trustees of Reservations and town personnel agree an offshore breeze will be necessary to send the man-of-war away.

"If we get a north wind or more of a west wind, where these jellyfish can be blown away from the shore, that would be really helpful," Mr. Egan said.

He said he has seen other items washing up on the beach as well.

"We've picked up three coconuts in this past week," Mr. Egan said, a rare but not unprecedented occurrence. "We're also seeing a fair amount of trash coming up."

This is the earliest in the season that beach managers can recall seeing man-of-war on the Island.

"We do get them, but usually it's later in the season," said David Belcher, who has been superintendent for The Trustees of Reservations' Chappaquiddick properties for 18 years. "It's the first time I've seen them this early. We don't usually get as many as we're seeing, either."

Southern-facing beaches still open for swimming have posted signs warning beachgoers not to touch the man-of-war. Washed up man-of-war and lone tentacles in the sand can sting as painfully as in the water. The signs also ask visitors to report wash-ups to guards, who will remove the creatures with a shovel and throw them in the dunes, where they will dry out and die.

Warning signs will remain posted at Lucy Vincent and Squibnocket even after swimming is permitted again, Ms. Pietruska said.

"They're so beautiful, it's something a child might be attracted to," Edgartown park administrator Marilyn Wortman said of the man-of-war. The translucent bodies of man-of-war can be tinted pink, blue or violet. In the water, they may look like a bag floating.

The warnings are also geared toward adults unfamiliar with the potentially dangerous sea animals.

"Many people that come to the beach have never seen this before, and don't know the sting is very serious," Ms. Pietruska said.

The creatures' venomous sting leaves painful welts or rashes, often resembling a lashing from a bull whip. Rarely, a sting can cause an allergic reaction and anaphylactic shock, which can be lethal.

"There are certain signs that you'd want to send someone to the hospital for: if they have trouble breathing, increased pulse rate," Ms. Pietruska said.

"It's kind of like getting a bee sting," Mr. Egan said. "Some folks are not affected by it much at all; other folks can get a very severe reaction to the sting."

A study published this year by the Medical Journal of Australia found that applying hot water to the sting helps alleviate the pain and is more effective than ice. Thousands of stings from Portuguese man-of-war are reported each year in Australia.

The only real cure for a sting is time.

"There's nothing you can do to make the process any faster," Mr. Egan said. "What we tell people is to wash well - they may still have a tentacle on them." The tentacle may not be visible on the skin, he said. An antihistamine or calamine lotion can also help.