Tourists were forced away from Horseshoe Bay yesterday after dozens of jellyfish and Portuguese man o' war washed up onshore.

The Department of Parks made the decision to close the popular beach to swimmers after 15 people were stung before noon.

A spokesman for the Parks Department said: "What we had was, for various reasons, a mixture of marine life washing in.

"While lifeguards were attempting to relocate the jellyfish and man o' war, they were also being called to do first aid for stings."

While the Parks Department was using yellow flags to warn swimmers to be careful, many people were still in the water.

The spokesman said: "Our resources were being stretched, and we didn't want anyone hurt, so we closed the beach."

The main beach was closed completely while five lifeguards and two park rangers cleared the area, but after an hour Parks officials were able to reopen sections of the beach.

The small cove to the west of the main beach was less affected and remained open throughout the day.

While most of the jellyfish that pass through Bermuda waters are relatively harmless to humans, causing only minor irritation, the sting of a man o' war can be much worse.

The sting usually causes severe pain and red welts that can last for several days, but larger quantities of the venom can cause fever, shock and, in rare cases, even death.

While often mistaken for a jellyfish, the man o' war is not actually a jellyfish, but a colony of several, specialised organisms living together that work with each other to survive.

Because they are often mistaken, people commonly treat the stings the wrong way. While jellyfish stings are often treated with vinegar, recent studies have found that adding vinegar to a man-o-war sting can actually make it worse.

The best treatment for a man o' war sting is to remove the stinger, being careful not to touch it further, and then apply salt water to the area affected.

If the pain persists, or if there is a severe reaction, it is recommended that you see a doctor.

While it is not uncommon for man o' war to drift onto Bermuda's beaches, the spokesman said it is very rare for enough to wash in to cause a beach to be closed.

"Most beach closures we have are due to the weather," said the spokesman.

"It's not common for a beach to close because of marine life, but every once in a while it happens."