The Ord River Irrigation Scheme (ORIS) was constructed on the river in 1963 and opened on June 30, 1972 by Prime Minister William McMahon. The scheme created Lake Argyle, which is Australia's largest dam, covering an area of 741 kmē.
ORIS provides water for irrigation to over 117 kmē of farmland and there are plans to extend the scheme to allow irrigation of 440 kmē in the future. The dam also generates power for the local community of Kununurra.
From the web at; http://en.wikipedia.org/wiki/Ord_River