For many years, large areas in the Eastern Cape experienced severe water shortages because of little rainfall in the arid Karoo.

The Orange–Fish Tunnel, together with its network of canals, weirs and balancing dams, has enabled these areas to be restored and has made the irrigation of thousands of hectares of additional land possible.

The main purpose of the tunnel is to divert water from the Gariep Dam to the Eastern Cape Karoo for irrigation, household, and industrial use.

It rises in the Drakensberg Mountains of Lesotho and flows Westwards through increasingly drier country to discharge into the South Atlantic at Oranjemund, where, through evaporation and abstraction, the volume was far less than it was at the location of the Gariep Dam.

Construction started in 1966; preliminary works included a tarred road running parallel to the route of the tunnel, and three towns, Oviston at the North end, one in the middle called "Mid-shaft", on the watershed plateau some 600 feet higher than on either side, and "Teebus" at the South end.

These towns included such facilities as a clubhouse, tennis courts, a community hall, primary school, clinic, etc.

The lining was done using a travelling shutter - concrete arrived first thing Monday morning, and continued unstopped until Saturday afternoon.

[8] The Contractor on the Inlet Section was Batignolles-Cogefar-African Batignolles, a consortium of French, Italian, and South African firms.

The Outlet Section was contracted to J. C. I. di Penta, a consortium that was formed by two firms - Johannesburg Consolidated Investment Company (JCI) from South Africa, and Impresa Ing.

[9] The intake tower is situated on the south bank of the Gariep Reservoir at Oviston, approximately 19 km (12 mi) upstream of the dam wall.