It flows south between the Neumann and Ohau ranges for 45 kilometres (28 mi) from its source on the west slope of Mount Edgar Thomson,[2] in the Southern Alps, before joining with the Hopkins River, close to the latter's entry into the northern end of Lake Ōhau in the Mackenzie Country.

[3] The river flows over wide shingle beds, and has no rapids of interest to whitewater enthusiasts.

[4] It was named by Julius von Haast in the 1860s for his father-in-law, Edward Dobson, who was the Canterbury Provincial Engineer.

[5] The Māori name, also given as Otao in some works, means "driftwood," and has also been applied to the Hopkins River into which the Dobson/Ōtaao flows.

[6][7] The New Zealand Department of Conservation maintains a tramping track and several backcountry huts in the river valley.