David Walliams may have suffered from the polluted waters of the River Thames on his recent charity swim, but some creatures seem to be thriving. Evidence of a colony of short-snouted seahorses has been found in the Thames, during a routine fisheries survey at Greenwich. This is the first time that these rare creatures have been found so far up the Thames and the first time in this part of London. Seahorses have always been visitors to the coastal waters around the British Isles but more recent sightings suggest that there may be more permanent populations around the UK. Normally found along the south coast of England, with substantial populations around the Channel Islands and Ireland, the creature's preferred habitiat is shallow muddy waters, as found in estuaries or inshore amongst seaweed and seagrasses, clinging by the tail or swimming upright. This particular species, Hippocampus hippocampus can also be found in rocky areas.

In 2008 they were protected under the 1981 Wildlife and Countryside Act, prior to this a handful of individuals had been found in the River Thames. This raised the possibility that the river may be supporting a colony, however they have not been found since and never this far inland.

The short-snouted seahorses can grow up to around 15cm and are relatively rare in the UK - the exact size and distribution of the population of seahorses around the British Isles is not known at present. . Seahorses are one of the few animals that mate for life after elaborate courtship rituals.

The Environment Agency has carried out regular monitoring of the fish populations within the Thames Estuary since the late 1980s. This data has enabled us to understand the importance of the river as a nursery and breeding ground for a number of species of commercial and conservation importance.

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. We routinely survey the Thames at this time of year and this is a really exciting discovery.

“We hope that further improvements to water quality and habitat in the Thames will encourage more of these rare species to take up residence in the river.“

The seahorse has a very distinctive shape with the head set at an angle to the body. The trunk of the body is short and rather fat whilst the tail is tapering, curled and prehensile. Hippocampus hippocampus is one of two species of seahorses found in the British Isles, the other is Hippocampus guttulatus, which has a longer snout and elongated protuberances along the back of the neck, giving the impression of a 'horses mane'.