Total water flow in the Murray–Darling basin 1885 to the present has averaged around per year. This is the lowest rate of the world's major river systems. About 6.0 percent of Australia's total rainwater falls into the basin. In most years only half of this quantity reaches the sea and in dry years much less. Estimated total annual flows for the basin have ranged from in 1902 to in 1956. Despite the magnitude of the basin, the hydrology of the streams within it is quite varied.