In the wet season it starts just south of the Arnhem Highway,[1] at about 30 m (98 ft) and flows 29 km (18 mi) north to Darwin Harbour.

It runs over Quaternary rocks, with poorly drained saline muds and clay plains.

Each wet season these plains are flooded by fresh water to depths of up to 2 m (6 ft 7 in) deep, for 6 to 8 months.

The valley has many lifestyle blocks, which, with demands from crops such as mangoes, has depleted the Koolpinyah dolomite aquifer, as over 2,000 wells have been sunk since 1960.

It was open savanna dominated by woolewoorrng, Corymbia jacobsiana and a sorghum grassland understory.