The water vole is to be protected in a new 22,000 acre Site of Special Scientific Interest (SSSI) on the Kent and East Sussex coast.
The new SSSI takes in Romney Marsh and areas of shingle beach
Dungeness, Romney Marsh and Rye Bay SSSI is the first in England created especially to save the water vole.
The vole, on which "Ratty" in The Wind in the Willows was based, is in danger of vanishing from 94% of its habitats.
Dungeness, Romney Marsh and Rye Bay SSSI, unites eight existing sites, and includes five acres of new designation.
The area's shingle beaches, sand dunes, grazing marshes and soil patterns are of national and international importance.
EIGHT EXISTING SSSIs
Camber Sands and Rye Salting
The site is home to Britain's only population of the Sussex Emerald Moth.
"This decision will ensure that the exceptional natural resources of the area are recognised and sustained for future generations," said Ben Fraser, of English Nature.
"The new site incorporates all of the key areas used by large numbers of water birds, allowing us to properly protect and manage habitats for them throughout the year.
"In addition, the vast network of wetlands provide habitats for many rare and threatened species, including the water vole, great crested newt, medicinal leech and greater water-parsnip."
The new SSSI includes evolving stretches of coastline between Winchelsea Beach near Rye and Greatstone, north of Dungeness.
One of the existing eight SSSIs, Cheyne Court, is to be the site of a 26-turbine wind farm, given permission after a public inquiry in 2004.