Thames Water has spent £250,000 improving the habitat and restoring conditions along a 1.5km stretch of the river, close to Waddesdon, and is now ready to restore 20,000 native fish.

The necessity for the works came when a leakage from the Aylesbury sewage treatment works polluted the stretch in 2002, damaging the river's delicate ecosystem.

But now the waters have been returned to their former glory - with a few added extras designed to improve on Mother Nature.

"Whilst any pollution incident is to be regretted I am pleased that Thames Water is making such a significant contribution towards improving the fish stocks and spawning grounds of this lovely little river," said Martin Salter MP, Parliamentary Spokesman for Angling. "This project is giving Mother Nature a helping hand."

A number of new features have been included in the scheme, including refuge channels in the river which will encourage fish to breed. Five gravel bedded riffles have been created to entice new fish species to breed and live.

It is hoped that local wildlife will also benefit from areas to designed to encourage river-dwelling creatures, such as water voles, to breed.

In addition, the enhancements to the river will enable up-stream fish migration, which has not been possible for over 120 years.

Species of new fish introduced to the river will include Chub, Roach, Bream, Perch and Gudgeon. They will be released gradually into the river under the supervision of the Environment Agency.

Thames Water's Director for Sustainability, Richard Aylard said: "We believe this will make a tremendous contribution to the health of the river and add to the enjoyment gained by its many users. This project demonstrates the importance Thames Water places on our responsibility to the environment."

The project has been joint initiative involving Thames Water, the Environment Agency, the Thame Valley Fisheries Preservation Consultative, Waddesdon Estate and the Ernest Cooke Trust.

Since the leak, efficiency and water quality discharge standards at the Aylesbury sewage works have been improved.