The Broads are Britain's largest protected wetland and are home to a wealth of wildlife, especially fish and birdlife. They comprise a network of mostly navigable rivers and lakes in the English counties of Norfolk and Suffolk. The lakes (or broads) were originally formed by the gradual natural flooding of medieval peat excavations and cover an area of some 303 square kilometres (117 sq mi). The rivers and broads subsequently evolved to become a system of water-highways linking the City of Norwich and other inland towns such as, Beccles, Belaugh and Barton with the sea-ports of Great Yarmouth and Lowestoft. This is also where the unique Norfolk Wherry, with its shallow draught and distinctive gaff rig with a single, high-peaked sail carried goods and passengers around the Broads area.