While obviously named after one of the English River Derwents, the name - which apparently means "valley thick with oaks" - is especially appropriate. When first explored by Europeans, the lower parts of the picturesque valley were clad in thick she-oak forests, remnants of which remain in a few places.
180 km long with flows ranging from 50 to 300 tonnes per second, its large estuary forms the Port of the City of Hobart - often claimed to be the deepest sheltered harbour in the Southern Hemisphere; some past guests of the port include the USS Enterprise and USS Missouri. The largest vessel ever to visit Tasmania was the 109 000 tonne ocean liner Star Princess, which made its first visit on 1st December 2003.
Until the construction of several hydroelectric dams between 1934 and 1968, it was prone to frequent flooding. The State of Tasmania is now almost entirely powered by hydroelectricity. A substantial part of the dam construction work was performed by Polish and British migrants after World War II.
Several bridges connect the western shore (the more heavily populated side of the river) to the eastern shore of Hobart - in the greater Hobart area, these include the five lane Tasman Bridge, near the CBD, just north of the port; the four lane Bowen Bridge; and the two lane Bridgewater Causeway.