The Broads is a network of mostly navigable rivers and lakes in the English counties of Norfolk and Suffolk. The lakes, known as broads, were formed by the flooding of peat workings. The Broads, and some surrounding land, were constituted as a special area with a level of protection similar to a national park by the Norfolk and Suffolk Broads Act 1988. The Broads Authority, a special statutory authority responsible for managing the area, became operational in 1989. The area is 303 square kilometres, most of which is in Norfolk, with over 200 kilometres of navigable waterways. There are seven rivers and 63 broads, mostly less than 4 metres deep. Thirteen broads are generally open to navigation, with a further three having navigable channels. Some broads have navigation restrictions imposed on them in autumn and winter, although the legality of the restrictions is questionable. Although the terms Norfolk Broads and Suffolk Broads are used to identify specific areas within the two counties respectively, the whole area is frequently referred to as the "Norfolk Broads".