The scheme, at Hesketh Out Marsh, has created habitats for estuary dwelling species including lapwing and avocet.
Jaye Rogers from the RSPB said the money would "result in the best for the estuary's ecology".
Hesketh Out Marsh, once an area of farmland, was flooded in 2008 to return it to wildlife-friendly saltmarshes.
The project has improved the local sea defences and created 150 hectares of new saltmarsh, creeks and lagoons.
Saline lagoons can be created to hold pools of water at low tide, creating elevated ridges to provide high tide refuges for many species.
Avocets and redshanks are among the birds that have already nested on the site and large numbers of lapwings, golden plovers, shelducks, wigeons and teals are expected to use the site in the winter months.
A project to restore saltmarsh on the Ribble estuary in Lancashire has received a grant of nearly £50,000 from the Landfill Communities Fund.