Much of Belarus (formerly the Belorussian Soviet Socialist Republic of the USSR, and then Byelorussia) is a hilly lowland with forests, swamps, and numerous rivers and lakes. There are wide rivers emptying into the Baltic and Black seas. Its forests cover over one-third of the land and its peat marshes are a valuable natural resource. The largest lake is Narach, 31 sq mi (79.6 sq km).