The western boundary of the hundred runs from North Fambridge to a bit west of Maldon. At the eastern end of the Dengie Peninsula is a large and remote area of tidal mud-flats and saltmarshes between the adjacent Blackwater and Crouch Estuaries.

These are the largest continuous example of its type in Essex. Foreshore, saltmarsh and beaches support an outstanding assemblage of rare coastal flora. It is of importance for wintering populations of Hen Harrier Circus cyaneus, wildfowl and waders.