Despite the fish's reputation, conservationists have said that the presence of the fish in the Thames is the sign that pollution levels in the river are going down.
The Thames was so disgustingly polluted - due to the fact that all types of dirty industries poured their waste into the water (and it was not uncommon to see dog and cat corpses floating in it) - that it was declared dead in 1950.
Poisonous Mediterranean fish found living in the Thames
By David Derbyshire
03rd October 2008
Bathers beware, this new arrival has a sting that's even uglier than it looks.
The greater weever, which grows up to 20in long with venomous spines, has turned up in the Thames for the first time.
The fish lurks below the seabed and if stepped on causes swelling, redness and pain for up to two weeks.
You might think he looks cute: A greater weever like this has been found in the Thames and will cause you pain for weeks if you step on its venomous spines
They can even kill. In 1927, a fisherman died after suffering multiple-greater weever stings.
But conservationists who discovered the fish at Tilbury in Essex said the monster's arrival was good news, and a sign of falling levels of pollution in our waters.
It was the sixtieth new species to be recorded by a two-year study into fish numbers in the Thames for the Environment Agency and London's Zoological Society.
Agency spokesman Tom Cousins said: 'Fish have been coming back
'In the 1950s, there were some areas that were dead - there were no fish at all because of sewage discharges and industrial pollution.
'But now we have around 125 species.'
The weever: A positive sign for the Thames - but bathers beware
He said the greater weever did not pose a serious threat, but warned bathers to take care at the seaside or when paddling.
Greater weavers hide in muddy, sandy or gravely sea beds, with just their fins showing and jump out at small fish and invertebrates. They are sandy coloured, up to 20 inches long and have large heads with savage teeth.
But their most dangerous feature is the poison spines that line their dorsal fins. If the spines are trodden on, the pressure sends a jet of toxin spurting upwards through the skin.
Not only are they are menace for divers and bathers, they can sting unsuspecting fishermen.
The discovery is a sign that the Thames is getting healthier since the heyday of pollution in the 1950s
The venom breaks down above 40C so the best treatment is to put a foot in hot water.
Matthew Gollock, Zoological Society of London's Thames conservation project manager, said: 'Heavy pollution in the Thames estuary once left the waterway devoid of fish species.
'However, the discovery of this new species and the blossoming diversity of fish are hugely indicative of the renaissance of the estuary.'
Unusual species such as the short-nosed seahorse and edible olive-yellow coloured John Dory fish have been found, along with well-known sole, cod, sea bass and thornback ray.
All of these species have been caught in the tidal Thames between Fulham and Tilbury since 1964.
ENGLAND'S GREAT RIVER
1) The Thames is a home for swans. King Richard the Lio0nheart first introduced swans to the Thames from Cyprus in the 12th Century.
2) Thames water is, believe it or not, drinkable (though this was definitely not the case until very recently). If you scooped a glass out of the river and left the silt to settle overnight, the water would be clean enough to drink! We don't recommend you try it though…
3) The river Thames begins life as a trickle in a Gloucestershire meadow and flows for over 217km (135 miles) though the Cotswolds, Oxford, Henley and Windsor before it reaches London
4) England's largest river is the Severn, but that also flows through Wales. The Thames is the largest river wholly in England.
5) There are 33 bridges over the Thames.
6) The Thames Path is the longest riveride walk in Europe - it is 184 miles long.
7) London has more World Heritage Sites than any other city on Earth: the Palace of Westminster (Houses of Parliament), the Tower of London, Maritime Greenwich and Kew Gardens - and they're all along the river.
8 )The Romans knew the Thames as Tamesis. The name may have originally come from the Latin for "wide water" or the Sanskrit word meaning "dark water".
9) The river used to be incredibly dirty because it was where all waste from London ended up. In 1858 the stench became so bad it was known as "The Great Stink." MPs in the Houses of Parliament even had to soak the curtains of the windows in chloride of lime while many members considered relocating parliament temporarily to Hampton Court.