It is a National Nature Reserve established by English Nature and in the care of the Norfolk Wildlife Trust.
It is also part of the Upper Thurne Broads and Marshes Site of Special Scientific Interest.
It is the largest broad, only 1.5 m deep, and has 586 hectares of open water, making it one of the largest expanses of open water in East Anglia.
It has the largest reed-bed in England and supports rare waterweeds such as the holly-leaved naiad and three rare species of stonewort. Amonst the rare insects is the swallowtail butterfly which feeds on milk-parsley, the Norfolk hawker Aeshna isosceles and emperor dragonfly.