The Grey River / Māwheranui is a major river system draining a large area of the West Coast of New Zealand's South Island. It originates in Lake Cristobel among the small lakes on the western side of the Southern Alps, approximately 12 kilometres southwest of the Lewis Pass. The river flows through diverse landscapes, from remote headwaters to a meandering incised gorge, before entering the Tasman Sea at Greymouth. Its mouth is protected by the Greymouth bar, a large sandbar that is a notorious shipping hazard. The river is protected by a Water Conservation Order, recognized for its outstanding natural characteristics, including the incised river gorge and scenic features.