Life in the Thames ( dolphins, seals and Darren the catfish.
Dolphins, seals and porpoises have all been spotted enjoying the famous waters, while sperm whales ( which grow to 14 metres ( have been seen in the Thames Estuary.
Ten years ago, a minke whale died after becoming stranded on the shore of the Thames at Purfleet, Essex.
A survey last year found most people believed shopping trolleys and sewage are the items most likely to be found in the river.
But a family of harbour porpoises were once spotted feasting on fish off Vauxhall Bridge in the centre of the capital, while common seals have been regular visitors to the waters around Canary Wharf, the Thames Barrier and near Tower Bridge.
Dolphins have been reported enjoying the waters near Southend in Essex, just inside the mouth of the river.
A survey by the Zoological Society of London (ZSL) last year received 103 sightings by the public of a total of 197 animals in the river, mostly near the estuary.
That included more than 100 seals, 62 porpoises and 18 dolphins. And in 2001, a giant catfish was believed to have escaped into the river.
The operation to land the 5ft- Wels catfish, which weighed 40lbs and was nicknamed Darren by locals, began after fears he could decimate other wildlife in the River Darent at Eynsford, Kent.
But a further survey last year for ZSL found 83% of those questioned in the capital and south-east held a bleak view about the river's contents.
It found 17% thought salmon was most likely, while just 6% believed there might be Dover sole ( even though the estuary is one of the most important nursery grounds for the fish.
Some 93% of those surveyed felt that the Thames was an important part of their city, yet many showed they were ignorant of its aquatic life.
The river seems to have been unable to shake off its dirty image for a majority of Londoners, who think its murky waters show the Thames is polluted.
In reality, over the last 30 years, the Thames Estuary has become one of the world's most unpolluted metropolitan highways, but its rich variety of wildlife remains a well kept secret.
Commercially important fish species, such as Dover sole and sea bass, use the Thames as spawning and nursery grounds. The estuary's mud flats provide essential feeding grounds for internationally important migrant bird populations.