Lake Mapourika is a kettle lake. It was formed when a large block of ice was left behind by the retreating Franz Josef Glacier some fourteen thousand years ago. It is ten kilometres north of the Franz Josef Glacier Village on the State Highway. It is the largest lake in the Westland Tai Poutini National Park. The lake is fed by a number of small streams that come from the surrounding bush clad hills. It drains into the Okarito River.