Ouse Washes is a linear 2,513.6-hectare (6,211-acre) biological Site of Special Scientific Interest stretching from near St Ives in Cambridgeshire to Downham Market in Norfolk. It is also a Ramsar internationally important wetland site, a Special Protection Area for birds, a Special Area of Conservation and a Nature Conservation Review site, Grade I. An area of 186 hectares between March and Ely is managed by the Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire and another area near Chatteris is managed by the Royal Society for the Protection of Birds. The Wildfowl & Wetlands Trust manages another area near Welney.

The Wildfowl & Wetlands Trust (WWT) is an international wildfowl and wetland conservation charity in the United Kingdom.