The Murray Darling Basin is located in southeastern Australia and consists mostly of the states of New South Wales. It has a semi-arid north and northeast and a warmer semi-arid south due to proximity to the southern Pacific Ocean. The two largest rivers are the Murray and Darling Rivers, which originate in the Australian Alps along with other tributaries. The basin itself is a flat plain located in the Murray Darling Depression, which was formed around 50-60 million years ago when the region was a shallow sea.