The Environment Agency will release 5,000 juvenile fish into the River Wandle in an attempt to rejuvenate the waterway which was devastated by pollution earlier this year.

Fisheries officers will release the fish at three areas along the river tomorrow, marking the first stage of a long term restoration process.

The batches of one to two year-old chub, dace, roach and barbel have been specially reared and trained for life in the wild at Calverton Fish Farm in Nottinghamshire.

A chemical spill killed tens of thousands of fish of varying ages, sizes and species along a five kilometre stretch of the river between Beddington and Merton in September.

Post-pollution survey work showed some species of fish were completely wiped out in the upper reaches of the river, closest to the pollutant's origin.

The Environment Agency has worked closely with anglers, the Anglers Conservation Association, the National Trust, the Wandle Trust and independent surveyors to determine the impact and decide the most effective way to rehabilitate the river.

Theo Pike of the Wandle Trust said: "The recent surveys have confirmed the serious impact of the pollution, but they have also demonstrated that there is adequate food and shelter for this limited initial restocking.

"This is important because we need to give nature a helping hand to restore fish stocks as there are many barriers to the free movement of fish up and down the river, meaning natural re-colonisation would be very slow."

Fisheries officer, Tom Cousins, said: "It will take several years before these fish will be of a size to be of interest to recreational fishermen, and many years before they approach the size of those fish lost in the pollution incident."

Mike Denbigh, team leader for the Environment Agency, said a case file was being prepared for the organisation's legal department.

"With incidents of this severity it is the Environment Agency's policy to fully investigate the incident and seek to prosecute," he said.