The Wash is a shallow natural rectangular bay and multiple estuary on the east coast of England in the United Kingdom. It is an inlet of the North Sea and is the largest multiple estuary system in the UK as well being the largest natural bay in England and is the outflow for the rivers Witham, Welland, Nene and the Great Ouse. It is also one of the most important places of conservation in Europe, with several nature reserves located within this area.