A friendly bottlenose dolphin that has been swimming off the Kent coast since last year was seriously injured when part of her tail was cut off.
Dave the dolphin has become very used to human contact
The female dolphin, named Dave, is thought to have suffered the injury in a collision with a boat propeller.
It follows warnings from animal welfare and rescue groups that she was at high risk of such an accident.
The British Divers Marine Life Rescue said the next few days would be crucial amid fears an infection could set in.
Spokesman Tony Woodley said volunteers would be keeping "a very close watch" on Dave's behaviour to see if she deteriorates.
Dorsal fin injury
Mark Simmonds, director of science for the Whale and Dolphin Conservation Society (WDCS) has urged boat-users not to go near the dolphin.
"This latest wounding follows the deaths of two other friendly dolphins in the UK last year and we really must learn to treat these animals with more respect.
"We are currently just killing them with 'kindness' by first taming them and then not looking after the tamed animals," he said.
Dave has been living in the Channel off Sandgate since last April and has become so used to human contact that swimmers have been seen trying to ride on her back.
In August, it emerged that she had sustained cuts on her dorsal fin, also believed to have been caused by a propeller from a boat.
Experts said it was not considered to be life-threatening, but warned it could lead to an infection which could prove fatal.