A 105-acre watery wilderness is being created in west London that includes a marsh, a large reed bed, a series of lakes and an extensive network of ponds.
This is The Wetland Centre, Barnes, the pounds 16m dream - now being realised - of Sir Peter Scott, the late naturalist, painter and founder of the World Wildlife Fund (now called the World Wide Fund for Nature).
Birds that normally steer well clear of cities, such as reed warblers and little ringed plovers, have already bred plentifully at the new centre; wild ducks and geese flock there by the hundred; a third of Britain's dragonfly species can be seen.
Sir Peter, whose wildfowl sanctuary at Slimbridge on the Severn became world-renowned, believed that a similar reserve could be set up in London, where it could serve as a powerful tool for environmental education.
Shortly before his death in 1989, he found the ideal site: a group of four Victorian reservoirs in west London owned by Thames Water but made redundant by a new large-scale water carrier, the Thames ring main.
He painted his impression of what they might become in his final painting (uncompleted on his death and finished by the artist Keith Shackleton).
A decade later, the transformation into what is believed to be the world's first real wetland in a capital city is nearly complete - thanks to an unusual three-way partnership between the water company, a housing developer and an organisation Sir Peter founded, the Wildfowl and Wetlands Trust (WWT).
Thames Water sold almost a fifth of the 125-acre site for housing to Berkeley Homes, which provided the pounds 11m cost of breaking up the four huge concrete and clay boxes that were the reservoirs and turning them into a series of wetland habitats with controllable water levels, to the WWT's design. The fitting-out of buildings will cost another pounds 5m, of which pounds 2m has already been raised.
The Wetland Centre will open in a year's time, but it is already clear that it will be a nature reserve to equal some of the most exciting in Britain, such as Slimbridge itself or the Royal Society for the Protection of Birds reserve at Minsmere in Suffolk.
The plate-glass windows of the visitor centre, 25 feet high and 100 feet long, look directly on to a large shallow lake which last week was crowded with flocks of teal, Britain's smallest duck. On the leeward side of a small island, a dozen herons hunched in shelter from the wind. Many wintering ducks, such as pochard and shoveller, are currently occupying the lakes: in January, 50 species of birds were recorded.
Out on the reserve, two main hides overlook a mosaic of habitats designed to bring in as great a variety of birds and other wildlife as possible. One of the hides is three storeys tall and is believed to be the only one in the world with a lift, which is to be used for disabled access. Closed-circuit television will be installed throughout the site.
The WWT is expecting 350,000 visitors a year to The Wetland Centre, and one of its prime purposes will be education: a series of exhibits will inform people about river life of the Thames and about wetlands around the world.
"Sir Peter thought the future of wetlands lay in education," said Kevin Peberdy, 35, the project manager. "He thought a major part of conservation lay in the education of people and he wanted to attract people to a nature reserve who wouldn't normally go. So rather than creating reserves in isolated places where the birds were, he thought we should go where the people were, and bring the birds to them."