Redgrave and Lopham Fens

Redgrave and Lopham Fens is a 127 hectare biological Site of Special Scientific Interest between Thelnetham in Suffolk and Diss in Norfolk. England. It is a national nature reserve, a Ramsar internationally important wetland site, a Nature Conservation Review site, Grade I, and part of the Waveney and Little Ouse Valley Fens Special Area of Conservation. It is managed by the Suffolk Wildlife Trust.

It is the largest remaining area of river valley fen in England and consists of a number of different fen types, including saw-sedge beds, as well as having areas of open water, heathland, scrub and woodland. It is also one of only three sites in the UK where the fen raft spider (Dolomedes plantarius) is known to be found.