Beginning in the west, the geography of Otago consists of high alpine mountains. The highest peak in Otago (and highest outside the Aoraki / Mount Cook area) is Mount Aspiring / Tititea, which is on the Main Divide. From the high mountains the rivers discharge into large glacial lakes. In this part of Otago glacial activity – both recent and very old – dominates the landscape, with large 'U' shaped valleys and rivers which have high sediment loads. River flows also vary dramatically, with large flood flows occurring after heavy rain. Lakes Wakatipu, Wanaka, and Hawea form the sources of the Clutha, the largest river (by discharge) in New Zealand. The Clutha flows generally to the southeast through Otago and discharges near Balclutha. The river has been used for hydroelectric power generation, with large dams at Clyde and Roxburgh. The traditional northern boundary of the region, the Waitaki River, is also heavily utilised for hydroelectricity, though the region's current official boundaries put much of that river's catchment in Canterbury.