The Site on the coast of south Essex in eastern England is composed of two river estuaries. The River Crouch occupies a shallow valley between two ridges of London clay, while the River Roach is set predominantly between areas of brick earth and loams with patches of sand and gravel. The intertidal zone along the two rivers is “squeezed” between the sea walls running along both banks and the river channels, leaving a relatively narrow strip of tidal mud which, nonetheless, is used by a significant number of birds. The Site is of importance for wintering waterbirds, with over 25,000 individuals regularly recorded. Among these the dark-bellied brent goose (Branta bernicla bernicla) is present in internationally important numbers. Additional interest is provided by a range of aquatic and terrestrial invertebrates and by an outstanding assemblage of nationally rare plants. The Site is an integral component of a suite of important nature reserves located along the mid-Essex coast. Within the Site there is a farm which serves as an educational facility and provides information about wildlife and the countryside. The local wildlife trust has two reserves on the Site, at which they conduct conservation education.