The South Island of New Zealand is home to three major rivers: the Grey, Buller, and Clutha. The Grey River is a short river that flows through the West Coast region of the South Island. The Buller River is a longer river that runs through the northern part of the South Island. Finally, the Clutha River is the longest river in New Zealand and runs through the southern part of the South Island. All three rivers are important sources of water for the people and wildlife of the South Island.