A multi-million pound grant has been awarded for the purchase of land to expand and recreate 9,100 acres (3,700 hectares) of Cambridgeshire wetland.
The project will see Woodwalton and Holme fens linked
The £8.9m support was given to the Wildlife Trust to buy almost half the land needed for the Great Fen Project.
The conservation scheme aims to provide a haven for a wide variety of wildlife that was once common in the fens.
The Heritage Lottery Fund awarded the sum which it said is its largest grant for a natural project in England.
The Great Fen Project in Cambridgeshire, run by The Wildlife Trust for Bedfordshire, Cambridgeshire, Northamptonshire and Peterborough, aims to eventually connect Woodwalton Fen and Holme Fen nature reserves.
'Reconnect with wildlife'
More than 99% of the UK's fens have been lost over the past 400 years, and the project aims to restore a large section of Cambridgeshire, between Huntingdon and Peterborough, back to a wetland landscape.
Actor Stephen Fry, president of the Great Fen Campaign, said: "I'm so thrilled at this news.
"The Heritage Lottery Fund has recognised the enormous value of the Great Fen Project and its unique, pioneering approach to this precious, delicate and beautiful landscape."
Organisers have already started to turn some fields back into wild wetlands, and the project aims to guarantee the future of fen meadows, reed beds and rare species only found in wetland habitats.
Michael Allen, chair of the Royal Society of Wildlife Trusts, added: "The promise of such generous funding enables us to take a significant step forward in our campaign to bring this important area of Fenland back to life.
"As nature gently begins to reassert itself in the area, new opportunities will be created for visitors to engage with the returning wildlife and to reconnect with the fenland landscape."