Coopers Lagoon / Muriwai is a small coastal waituna-type lagoon in the Canterbury region of New Zealand, located approximately half way between the mouth of the Rakaia River and the outlet of the much larger Lake Ellesmere / Te Waihora. While the present-day lagoon is separated from the nearby Canterbury Bight by approximately 100 metres (330 ft), the water of the lagoon is considered brackish and early survey maps show that, until recently, the lagoon was connected to the ocean by a small channel. The lagoon, along with the surrounding wetlands, has historically been an important mahinga kai (site of traditional significance for food and other natural resources) for local Māori.