For 10 points—name this longest river and water source of almost all arable land in Australia.
Used primarily for irrigation, its numerous hydroelectric plants include one on the Hume Reservoir. Flowing southwest through the lagoon of Lake Alexandrina, it runs into the Indian Ocean after receiving its main tributary, the Darling, at Wentworth. For 10 points—name this longest river and water source of almost all arable land in Australia.
Used primarily for irrigation, its numerous hydroelectric plants include one on the Hume Reservoir.
{Murray} River