inlet of the Tasman Sea, indenting southeastern Tasmania, Australia. About 16 mi (26 km) long and 25 mi wide, it is bounded by North Bruny Island (west) and the Tasman Peninsula (east) and opens into Norfolk and Frederick Henry bays to the northeast. The Derwent River estuary enters the bay from the northwest by way of Hobart. It was named by the Dutch navigator Abel Tasman in 1642 when a storm forced his ships out to sea before they could anchor there. The British explorers George Bass and Matthew Flinders sailed its waters in 1798–99.