The seal that was spotted in the River Dour on Thursday has still not been caught, and will not survive in its current surroundings.

Vet Jeremy Stattersfield was called to the scene in Dover at about 2pm yesterday after the sighting sparked a call to the police and the RSPCA.

After reports youngsters were throwing stones at it, the team attempted to catch it, but had no luck.

He said it is possible the seal, which is a pup, was separated from its mother during bad weather. But he has no idea how it got to the Dour.

Mr Stattersfield, who works at Burnham House Veterinary Surgery, said: “We tried to trace it in nets but the water level is very high at the moment.

“When it got dark we decided to back off but the RSPCA today have the help of Kent Fire and Rescue to try and catch it again.

“It is going to have to be rehabilitated,”he said.

“I don’t see how it got there to be honest, but it has such a lovely behaviour, they always do, especially the pups.”

Its gender is not yet known.

Nina Milton, of Alfred Road, first raised the alarm at 2pm, when she tweeted the police with the picture of the rare sighting.

Mrs Milton was leaving work at St Mary’s Primary School in Laureston Place when a colleague of hers thought she spotted a large fish next to the River Dour.

On closer inspection it was a seal that had moved under the bridge and had gone to sleep.

After alerting the RSPCA, they waited until help arrived.

She said: “I rang Dover police station and they were very helpful as they sent officers.

“The last I saw they were wading trying to catch it, but it was quick.”

The police confirmed that they were also called after receiving reports that youngsters were throwing stones at it and are investigating.