The lowlands west of australia's eastern mountain range are drained by the murray-darling river system, with its main headwaters in the great basin

The answer is - Artesian (Great Artesian Basin).

The mountain range in the eastern part of Australia is where the biggest rivers on the continent are gaining their waters from. The biggest of them are the Murray River and the Darling River. These rivers are heading towards the Great Artesian Basin where they create a big lake. This is lake is salty even though there's a constant new fresh water coming in because there's lots of salt on its floor which is a remnant from the time when this basin was part of the ocean.