Murray, principal and second-longest river of Australia, 1,609 mi (2,589 km) long, rising in the Australian Alps, SE New South Wales, and flowing westward to form the New South Wales–Victoria boundary. It then flows southwest across South Australia state through Lake Alexandrina, a lagoon, into the Indian Ocean. It receives its main tributary, the Darling River, Australia's longest river, at Wentworth. The Murray-Darling watercourse is 2,911 mi (4,685 km) long but is of little use for navigation except in the lower reaches. Used primarily for irrigation, the Murray has numerous hydroelectric plants and reservoirs, including Hume Reservoir. The Murray and the Murrumbidgee, a tributary and Australia's third-longest river, receive most of the diverted water from the Snowy Mts. Hydroelectric Scheme. The combined Murray-Darling basin supports more than 40% of Australia's agriculture, including more than 90% of domestic fresh food production.