Colonies of seahorses could be breeding in the inland stretch of the Thames, conservationists have said after a rare species was discovered.

In what is being described as a “really exciting” development, a short-snouted variety of the elusive creature was found during a routine fishery survey at Greenwich.

Environmentalists are confident that there will more colonies as the seahorse was a baby and the species live in numbers.

It is the first time that seahorses, or hippocampus hippocampus, have been seen so far up the river.

Emma Barton, Environment Agency fisheries officer, said “The seahorse we found was only 5cm long, a juvenile, suggesting that they may be breeding nearby.

“This is a really good sign that seahorse populations are not only increasing, but spreading to locations where they haven’t been seen before.”

The baby was released back into the river after being measured.

The animals – which are protected under the Wildlife and Countryside Act – are visitors to the country’s coastal waters but recent evidence suggests there are permanent populations around the UK.

Only a handful have ever been found in the Thames and never so far inland.