The Rangitata River, 75 miles in length, reaches the sea just north of Temuka and is formed by the confluence of two main tributaries, the Clyde and Havelock Rivers, which with their tributaries drain the eastern side of the Southern Alps from the Lyell Glacier to the Godley Glacier.
Other large tributaries are the Lawrence River, which drains the west side of the Arrowsmith Range, and Forest and Bush Streams, draining part of the Two Thumbs Range, and Potts River. These larger tributaries join the Rangitata in the large glacially excavated basin containing several sheep stations, including Mesopotamia Station, where Samuel Butler established himself in the early sixties.


