A major clean-up operation has begun on the Thames after a barge carrying 50 tonnes of fuel sank in south-east London, taking two tug boats with it.
No-one was hurt when the pontoons and work boats sank
Diesel has been spotted in the water from Woolwich to Wandsworth after the vessels sank near Cherry Garden Pier in Bermondsey on Tuesday morning.
The Port of London Authority (PLA) said one tank did not leak and a lot of oil from the other was safely pumped away.
Salvage teams have been out mopping up what they can using absorbent cloths.
It is thought that of the 50 tonnes of fuel carried by the barge, less than 10 leaked out - a PLA spokesman said the fuel was low-grade and less harmful.
The spokesman told BBC News: "Undoubtedly some of the oil will have leaked into the river.
"It is not the sort of oil which will form a slick but cause a sheen on the surface, but obviously we don't like any sort of oil entering the river.
"Our priority is to minimise any risk of pollution."
No-one was hurt when the pontoons, which are used by City Cruises to refuel their boats, sank in a storage area.
People living nearby were woken by the smell of diesel at about 0100 BST.
There are fears for the safety of birds by the river and other environmental concerns.
Barry Duckett, of Rotherhithe Angling Club, described it as a "catastrophe along the Thames".
And it is thought it could take weeks for the fuel to disperse - salvage crews are in the process of trying to raise the tugs and the barge to find out why they sank.
The Thames Clipper passenger services were not affected.