Lake Ohau, on the boundary between Canterbury and Otago, 112 miles by road from Timaru, has an area of about 23 sq. miles, and lies 1,704 ft above sea level. Its 460 sq. miles of catchment, which extend to the main divide of the Southern Alps, are drained principally by the Dobson and Hopkins Rivers and their numerous tributaries. The inflow varies between 400 and 13,700 cusecs, and averages about 3,000 cusecs. Unlike the other two Mackenzie Country lakes, Pukaki and Tekapo, Lake Ohau is not predominantly glacier fed, although there are small glaciers in the heads of the main valleys. The water is clear and cold (46°F). The present lake occupies the lower end of a glaciated valley and is confined by a moraine 16,000–18,000 years old.

The water level in Lake Ohau is not controlled, but the Ohau River contributes water to the Waitaki River on which is the 105-megawatt Lake Waitaki hydro-electric station. Other stations under construction or planned will also use water from the lake.

The name Ohau occurs frequently among Maori place names and the meaning usually accepted is the literal one, “windy place”.

by Leslie Eric Oborn, A.O.S.M., New Zealand Geological Survey, Christchurch.