It flows east across the upper Canterbury Plains from its source north of the town of Oxford, New Zealand, flowing into the Cam River / Ruataniwha close to the town of Rangiora.

[1] The lower part of the river, to the south-west of Rangiora, is diverted into a channel and called the "Main Drain".

[2] The channel was built in 1862 to drain the swampy land between Rangiora and the Waimakariri River, and when it was enlarged in 1868 it accidentally captured the Cust.

[3] The river was named in 1849 after Sir Edward Cust, a member of the Canterbury Association.

[4][5] Brown trout spawn in the river[6] and are suitable for fishing in spring.