SWIMMERS were evacuated from the water after a six-foot-long shark was spotted in the shallows at a Dorset beach.
Red flags were raised on the beach at West Bay, near Bridport, after the creature was spotted close to the shore.
Experts think the shark was probably a blue shark, an endangered species, rarely sighted in Dorset, which have been known to attack humans.
Dr Tom Brereton, research director of the charity Marinelife, said clearing the beach was the right thing to do.
He said: “Blue sharks can be dangerous, if provoked, and they have been known to attack people but normally they will swim off.
“It was sensible to clear the beach because there was a danger.
“If you see one and you are in the water don’t agitate the animal, go in the opposite direction.”
Dr Brereton said a fisherman had encountered a blue shark, probably the same animal, a few miles from the beach sighting.
He said: “On the same day a fisherman fishing for mackerel snagged a blue shark on his line, from the description of the beach sighting it sounded like the same one.
“Blue sharks are not normally found in Dorset waters, it’s fairly unusual to see them here so both sightings were probably of the same creature.
“The rising temperatures here have brought warmer water species to these waters so it’s worth keeping an eye out in the coming days.”
A spokesman for RNLI said: “We cleared the water.
“It’s standard procedure when we have a sighting like this – we have to respect the wildlife.
“The red flags went up and the beach was reopened after an hour and a half.
“It was open the next day – people were advised to stay close and not go out of their depth.”
She added: “Our lifeguards remained vigilant for other sightings over the next few days.
“We don’t know if it was a shark, if it was it may have been a blue shark shoaling for fish.
“It certainly wasn’t very big and we don’t want people to be alarmed.”
ADULT blue sharks can grow to 12ft in length and weigh 204 kilograms or 450lbs.
They mostly eat other fish, such as squid, mackerel and herring.
Blue sharks are considered to be a dangerous predator, believed to be responsible for attacks on humans in the past.
The species inhabits deep water in tropical, subtropical and temperate seas all over the world. Blue sharks travel hundreds of miles each year, migrating in large groups across the North Atlantic using the Gulf Stream.
Over-fishing has resulted in blue sharks, which have bright blue bodies with a white underside and large eyes, becoming an endangered species.