Barnby Broad and Marshes is a Site of Special Scientific Interest (SSSI) in the Waveney district of the English county of Suffolk.

[10] The site consists of a mixture of grazing marsh, carr woodland, fen and open water habitats stretching from the edge of the villages of Barnby and North Cove northwards across flood plains to the river.

[12] Flora found in and around the Broad includes the white water-lily Nymphaea alba, common reed Phragmites australis and the rarer tussock-sedge Carex appropinquata as well as species such as marsh arrowgrass Triglochin palustris and southern marsh-orchid Dactylorhiza praetermissa.

These cover the flood plain of the River Waveney from the edge of the wooded area to the south to the remains of Castle Mill in the north.

[13][14][15] The marshes are flooded in winter, providing overwintering habitat for bird species such as teal, shoveler and gadwall and breeding grounds for lapwing and common redshank.