According to a report in The Sun, the walking catfish, which was still alive, was discovered by baffled angler Birol Koca.
He called the Environment Agency who collected the fish in Woolwich, South East London.
They confirmed it was a catfish that can survive on land and uses its pectoral fins to 'walk'.
They are usually found in South-East Asia.
"I knew it should not be in our rivers," Koca said.
Fisheries officer Emma Barton said that the odd fish was probably dumped after growing too big for an aquarium.