The BBC's Paul Greer: "Thousands of dead fish were floating downstream"

A three-mile stretch of the river Wey in Hampshire has been contaminated by ammonia.

The Environment Agency, which has launched an investigation, says the fish population of the river between Alton and Bentley has been "completely devastated".

The area is popular with local anglers but they deserted the riverbank on Sunday as the potential catch floated on the surface.

Thousands of fish are dead because of the spill

Environment Agency officials were called to the scene on Saturday after a local resident noticed foam and a strong smell.

Cleaning up

A clean-up operation was under way on Sunday and the agency's spokesman said: "The pollution has affected a three-mile stretch of the River Wey between Alton and Bentley killing thousands of brown trout, chubb, roach, dace and perch.

"It has completely devastated the local fish population."

He said: "Samples taken by the agency have yet to confirm the pollutant, but initial investigations point to ammonia as the cause."

The agency says it has traced the source and is gathering evidence with a view to taking legal action.

Possible impact on food chain

It is also carrying out a full biological impact survey.

The Wey is fed by the Caker Stream, which runs adjacent to an industrial estate and a sewage treatment works, which has been ruled out as the source of the contamination.

The Ministry of Agriculture, Fisheries and Foods has advised farmers not to abstract water from the river but South East Water says there is no risk to the public drinking water supply.