Lake Mapourika is located on the West Coast of New Zealand's South Island, 10 kilometres north of Franz Josef Glacier. The Ōkārito River flows from Lake Mapourika to become the picturesque Ōkārito Lagoon before heading out to the Tasman Sea. While it is a popular fishing spot, the lake's dark tea-coloured water can make things a challenge. Rainwater filling Lake Mapourika flows through the dense forest before reaching the lake, collecting tannins from the forest floor along the way and turning the lake its dark colour.

Lake Mapourika is the largest of the West Coast lakes and is known as a kettle lake. Kettle lakes are formed when a large chunk of ice is left behind from the retreating glacier, and after the ice melts, the depression left behind fills to form a lake.