Trout bred by schoolchildren are giving a new lease of life to a once uninhabitable river.
The River Wandle runs from Croydon to Wandsworth
The Wandle, in south London, once dubbed a "sewer", has been restored to its former glory by environmentalists.
The first of thousands of baby brown trout are being introduced to mark the successful clean-up.
The trout, bred by pupils at the Old Palace School in Old Palace Road, Croydon, south-west London, will be released into the river on Monday.
Cleanest flowing river
There are plans for other London schools to become involved if the scheme proves successful.
About 300 years ago the Wandle, which runs from Croydon to Wandsworth, was a crystal clear chalk stream but became polluted by the tanneries during the industrial revolution.
Following the clean-up by the Wandle Valley Mapping Project, the river is now the cleanest flowing through any capital in Europe.
David Bellamy will help release the trout into the river.
Organisers also plan to reintroduce water voles, salmon and crayfish to the Wandle.