The Opihi River flows through south Canterbury, in New Zealand's South Island.

It flows southeast for 75 kilometres, reaching the Pacific Ocean 10 kilometres south of Timaru. The town of Fairlie lies on the river's banks.

The banks of the river around the settlement of Waitohi were possibly the site of the first powered heavier-than-air flight on March 31 1903 when pioneer aviator Richard Pearse is reputed to have got his home-made machine airborne several months before the Wright Brothers