The clean up of the Olympic Park site in Stratford will lead to a reduced flood risk for West Ham and Canning Town homes, environmental bosses promised today.

The Environment Agency announced the completion of an eight year project to transform 2.5km of land into Europe’s largest urban park for more than a century.

The agency said the operation involved making space for flood water and improving flood defences on the River Lea, meaning 4,000 properties were at a reduced flood risk.

The project, undertaken with the Olympic Delivery Authority (ODA), involved planting more than 300,000 wetland plants, 2,000 trees and cleaning 2m tonnes worth of soil.

Japanese knotweed, Himalayan balsam and floating pennywort was removed from five miles of the river. More than 22 miles of new cycleways and footpaths have also been built.

Lord Chris Smith, Environment Agency chairman, said the work had improved water quality, restoring habitats and reducing the flood risk.

He added: “This is a great example of how development and sustainability can go hand in hand, and I hope the same approach can be taken for other large infrastructure projects in the future.”

A sewage water recycling plant, and a low-carbon energy centre are already in place on the site.

Sir John Armitt, chairman of the ODA, added: “To have created Britain’s largest urban park for more than a century out of a contaminated, industrial landscape has taken both determination and clever thinking.”