London ? It’s a whale of a tale – a bottle-nosed whale swimming up the River Thames past Big Ben and Parliament on Friday as rows of worried Londoners looked on.

The northern bottle-nosed whale was spotted in central London in the afternoon – the first sighting in the river since whale-watching records began in 1913 – as it flailed around the murky waters of the Thames, stirring up patches of what looked like blood as seagulls hovered above and rescue boats stood on the ready.

Other witnesses reported seeing a second whale in another part of the river Friday, and marine experts spotted two disoriented whales off northeastern Scotland last week, suggesting something was causing bottle-nosed whales to become confused.

“It is a race against time to save the animal,” said Alison Shaw, marine and freshwater conservation program manager at the Zoological Society of London.

A small armada of rescue boats made frantic searches for the whale, which disappeared from view around sunset after diving under the surface of the water.

Crews barricaded a section of river in an attempt to force the animal to change course, and reports Friday evening claimed the mammal may be heading for safety.

Britain’s Maritime and Coastguard Agency said the whale was last seen at Chelsea Bridge – farther downriver from earlier sightings, meaning the animal could be moving back out to sea.

A whale swims Friday in the River Thames near the Houses of Parliament, top, in London. The bottle-nosed whale, which is about 17 feet long, drew scores of Londoners and television crews.

“A whale in the shallow water of the River Thames is like a human lost in the heat of the Sahara desert,” said Laila Sadler, scientific officer at the Royal Society for the Prevention of Cruelty to Animals. She estimated it could survive only for 24 to 48 hours in a river that has an average depth of between 26 feet and 20 feet.

“It also seems to be in distress; it has made two seemingly deliberate attempts to beach itself,” Sadler said.

Scientists have said fluctuating ocean temperatures, predators, lack of food and even sonar from ships can send whales into waters that are dangerous for the mammals.