Lake Pukaki is the second largest of three roughly parallel alpine lakes running north-south along the northern edge of the Mackenzie Basin (the others are Lakes Tekapo and Ohau). It covers an area of 80 km², and is at an altitude of 480 metres above sea level.

The lake is fed at its northern end by the braided Tasman River, which has its source in the Tasman and Hooker Glaciers, close to Mount Cook. Good views of the mountain, 70 kilometres to the north, can be had from the southern shore of the lake.

The lake's outflow is at its southern end, into the Pukaki River. The lake is an upper part of the Waitaki hydroelectric scheme, and as such, several dams and artificial canals are found near its outflow, linking it with lakes Tekapo and Ruataniwha.