The agency says the area, near the Slimbridge Wetland Centre, is of "international importance" for migrating wildfowl, breeding waders, migratory fish and Atlantic eels.
Bird haven Slimbridge in Gloucestershire, which is also the headquarters of the Wildfowl and Wetlands Trust, and the Dunes Coastal Park in the Outer Hebrides have also been short listed for the Best Environment Project award.
