The discovery of a seahorse in the Thames Estuary is a sign the river is becoming cleaner, experts said.
Seahorses have not been seen in the Thames estuary since 1976
The male seahorse was found by a fisherman trawling in shallow water off Leigh-on-Sea in Essex.
The sea creatures, which are mainly found in the warmer climate of the Bay of Biscay and the Channel Islands, have not been seen in the Thames since 1976.
Sea life expert David Knapp said the discovery was a sign the Thames was
getting cleaner and warmer.
Mr Knapp, who is looking after the seahorse at the Sealife Adventure Centre in Southend, said: "Everyone thinks the Thames Estuary is a polluted, dead river but that could not be further from the truth."
Mr Knapp said water companies have efficiently removed all contaminants from water discharged back into the river creating a haven for wildlife to flourish.
"We have seen an increase in all sorts of wildlife, not just fish but birds
"Little egrets and avocets which were very rarely seen in England a decade
ago are now quite a common sight along parts of the Thames."
The seahorse was handed to the centre two weeks ago by fisherman Brian Baker who noticed it among a clump of seaweed.
"At first he thought it was dead. He put it in a bucket of water and when he looked at it again it was swimming around quite happily," said Mr Knapp.
The seahorse, which is four inches long, is now sharing a 60-litre tank
with two hermit crabs.