The Tamar Estuary lies on the border between Devon and Cornwall on the southern coast of England. The estuary system is a large marine inlet on the English Channel coast comprising the estuaries of the rivers Tamar, Lynher and Tavy which collectively drain an extensive part of Devon and Cornwall. The Tamar river and its tributaries provide the main input of fresh water into the estuary complex, and form a ria (drowned river valley) with Plymouth lying on the eastern shore. The broader lower reaches of the rivers form extensive tidal mud-flats bordered by saltmarsh communities. The mud-flats contain extensive and varied infaunal communities rich in bivalves and other invertebrates, and feeding grounds for waterbirds in numbers of European importance. Saltmarshes provide important feeding and roosting areas for large numbers of wintering and passage waterbirds.