The Douglas River is a river of the West Coast of New Zealand's South Island. Its source is high in the Southern Alps, five kilometres south of Mount Sefton, and its upper reaches are fed by water from the Douglas Glacier, New Zealand. It flows west for 18 kilometres, joined by runoff from the Horace Walker Glacier, before joining the waters of the Karangarua River. The Douglas River's entire course is within Westland Tai Poutini National Park.