Forget the whale: what about the lamprey?

Thames dweller: a lamprey.
Photograph: Wes Stafford/APToday's sighting of hyperoodon ampullatus - a northern bottlenose whale to you and me - in the Thames for the first time since records began has caught the imagination of the global media, and some amusing headlines, including Ahoy, whale off Westminster Bridge! from the Globe and Mail in Canada, Thar she blows - right through London from Newsweek and the delightful ABC News headline Whale swims through downtown London. But it's by no means the first time that an unexpected animal visitor has caused ripples in central London.

Other exotic interlopers have included a red-bellied piranha last year (probably dumped from a domestic aquarium and swiftly killed by the cold water) an illegally imported 5ft long wels catfish (possibly). A total of 197 animals were seen in the river last year, according to a survey by the Zoological Society of London, more than 100 seals, 62 porpoises and 18 dolphins, although most of these were located close to the estuary.

There are no shortage of concerned groups trying to help the seemingly stranded whale - nicknamed Gonzo by the Thameside PR agency that has been following every fin-flap all afternoon in a specially-created blog. The Zoological Society of London has sent marine mammal veterinary pathologist, Paul Jepson, and the British Divers Marine Life Rescue, has launched a rescue boat. Meanwhile an RSPCA spokeswoman has urged the public to "be restrained and not to approach this animal" (fat chance, I suspect). Although Gonzo may not survive its sojourn in the Thames, the future is looking bright for the river's more routine residents.

Improvements to London's sewage systems have seen a big improvement in the quality of the water in the Thames, which has heralded the return of many creatures previously banished by pollution. Indeed, Thames Water says there are around 120 species of fish now present in the river.

For instance lampreys - a threatened species of parasitic fish - have returned to the Thames in the last two years, to the excitement of the Thames Explorer Trust, and the banks of the capital's river are billed as offering some of the best coarse fishing in the country.