Barnby Broad and Marshes is a Site of Special Scientific Interest (SSSI) in the Waveney district of the English county of Suffolk. The site is 189.6 hectares (469 acres) in size. It is in the parishes of North Cove and Barnby, located between Beccles and Lowestoft in the north of the county. The site is bordered on its southern edge by the East Suffolk railway line and to the north by the River Waveney. It is a Special Area of Conservation, a Special Protection Area under the EC Birds Directive, and a Ramsar internationally important wetland site. There are two Suffolk Wildlife Trust nature reserves in the site, Castle Marshes and North Cove.