Environment Agency chiefs are investigating the source of this oil slick running through the River Severn at Shrewsbury.

John Roberts, chairman and head bailiff of Shropshire Anglers Federation, said he had seen the slick between Station Bridge and Castle Walk Bridge.

He said the substance smelt like diesel. He said: “It is either from a diesel train spill off the Station Bridge or somebody has put something in the water.

“Somebody may have chucked a drum in.”

Serena Balsdon, a spokesman for the Environment Agency, said problems with an oily film on the water’s surface were first reported on May 18, when a caller reported a slick measuring approximately 50 metres moving down the River Severn.

“Our environment officers went out to investigate and went to Castle Bridge and found oil across the river.

“They walked down to the weir and found oil going over the weir.”

She said the source was not located and there were no sightings of dead fish.

The problem reoccurred this week, with the agency receiving four calls since yesterday from members of the public. “One caller cycled for about three-quarters of a mile and could still see the oily film most noticeable on the left hand side,” Ms Balsdon said.

“Our environment officers are currently at the site undertaking visual monitoring of the area to try and trace the source of the oily film. Once our investigations are complete, we should be able to provide more information.”

Councillor Alan Mosley went down to inspect the section of river in Castlefields after people reported seeing a strange substance in the river. “There is something floating around on the top of the surface,” he said.

“The river is pretty static at the moment so its not moving away very quickly.

“I hope the Environment Agency and council officials get down here and look at this very quickly, investigate and ensure this does not happen again in the future.

“They need to take whatever action necessary to ensure there is no repeat.”

By Chris Burn