Porpoises and seals are regular visitors to London, the first official survey of marine mammals in the River Thames has shown.
Thirty grey seals have been seen in the Thames
The Zoological Society of London (ZSL) received 103 sightings from the public since the survey began last July.
Porpoises were seen at Vauxhall Bridge, seals were spotted near Tower Bridge and dolphins seen at the mouth of the Thames estuary in Southend, Essex.
The ZSL is asking the public to continue to report sightings.
The survey reveals that since July 2004 , 197 marine mammals were seen.
Seals were the most frequently spotted marine mammals, with 46 common seals, 30 grey and 41 unidentified seal species being sighted.
Some 62 harbour porpoises were found to venture further up the estuary and the indications are that they remain in and around the estuary all year round.
The 18 dolphins sighted were only reported around the mouth of the estuary during spring and summer, suggesting that they are seasonal visitors.
Riverside pub patrons, commuters and river users have all been involved in gathering the essential survey information about these more unexpected Thames species.
Renata Kowalik, ZSL's conservation biologist and co-author of the report said: "The results confirm that marine mammals are frequent visitors to the Thames and have helped us to fill a gap in the current knowledge about the wildlife in the Thames."
"We hope that even more people will get involved this year and contact us with any sightings they have made."
Anyone wishing to take part can download a sightings form from ZSL's website.