England's wetlands are "vital" in helping people and wildlife adapt to an uncertain future, the Environment Agency's chairman said as he visited a project to restore areas of the habitat.
The fens in East Anglia were drained more than three centuries ago to provide fertile farmland, but green groups are now restoring some of the wetlands for their environmental benefits.
The Great Fen project near Peterborough and Wicken Fen, near Cambridge, are among a number of schemes around England which aim to restore wetlands and reverse declines in the habitat in the UK.
According to the coalition of conservation groups, wetlands can help people and wildlife cope with climate change - storing floodwaters and carbon and improving water quality.
They can be used as grazing areas for cattle and are home to half the UK's plant species, as well as providing refuge for endangered animals and birds such as water voles, bitterns and snipe.
But some 90 per cent of historic wetlands have been lost, and what remains is often isolated and poorly managed.
The Great Fen project aims to create a 3,700 hectare wetland linking two existing nature reserves, Holme Fen and Woodwalton Fen, between Huntingdon and Peterborough to create a haven for wildlife.
The Wicken Fen scheme will create a nature reserve covering some 53 square kilometres between Cambridge and Wicken Fen for people to enjoy and to protect the 7,800 species which live there.
Visiting Wicken Fen to mark World Wetlands Day, Environment Agency chairman Lord Chris Smith said: "Across England we've inherited only a few small and fragmented areas of wetland, often under pressure from pollution and development.
"Our remaining wetlands and their wildlife are deteriorating just as we are beginning to understand how vital they are in helping people and wildlife adapt to an increasingly uncertain future."
He said schemes such as the Great Fen and Wicken Fen projects, in which the Environment Agency is involved, would help manage the impacts of climate change and help threatened wildlife survive.
The projects form part of the Wetland Vision for England, in which the Environment Agency, the RSPB, English Heritage, the Wildlife Trusts and Natural England are restoring and creating wetlands across the country.
Other projects include work in the Somerset Levels and Moors, Morecambe Bay, the meres and mosses of Cheshire and Shropshire and the Humberhead Levels.