The Cook River / Weheka is in the South Island of New Zealand. The headwaters are from the La Perouse Glacier on the western flanks of the Southern Alps, and it flows west, then northeast, then northwest and into the Tasman Sea. Its tributaries include the Balfour River, fed by the Balfour Glacier, and the Fox River, fed by the Fox Glacier. Much of the river lies within the Westland Tai Poutini National Park.