The Mardoowarra (also known as Martuwarra or Fitzroy River) is a large, unregulated river system in the western Kimberley region of far north Western Australia, draining into King Sound near the town of Derby. The catchment spans arid terrain for most of the year, with the wet season transforming the landscape dramatically as floodwaters swell the river and spread across vast floodplains.

The most commonly documented paddling route runs from the headwaters area near Kupungarri/Mount Barnett — accessed via the Barnett River, a tributary — downstream to Fitzroy Crossing, where the Great Northern Highway meets the river. This stretch covers roughly 100 miles and has been completed by expedition teams using rafts and packrafts over approximately 14 days. Access to the headwaters typically requires a light aircraft, with flights departing from Derby. Fitzroy Crossing serves as the standard takeout point.

The river's character varies considerably along its length. Upper sections involve significant whitewater, including large rapids with powerful hydraulics, dumping waves, vortices, and water funnelling into underwater caves. Flat, slow pools — some stretching seven to eight kilometres — alternate with these whitewater sections, making progress variable and at times demanding. During the wet season, the river overtops its banks and spreads across the floodplain, creating disorienting conditions where paddlers can easily lose sight of the main channel and become stranded in flooded vegetation.

Wildlife encountered on the river includes freshwater crocodiles, bat colonies, and various birds. Saltwater crocodiles have not been confirmed for the upper sections, though paddlers should verify current conditions with local authorities. The wet season, roughly from late December through March, is when the river runs at its highest and most powerful, and is the primary window for expedition-style paddling. Late in the wet season — around March — has been the timing used by documented expeditions.

Within Danggu Geikie Gorge National Park, private boats are restricted to before 7:30 am and after 4:30 pm to avoid conflict with commercial boat cruises, and camping within the park is not permitted. The gorge itself, located near Fitzroy Crossing, has also been paddled as a shorter day trip of around 12 kilometres.

The river holds deep cultural and spiritual significance for multiple Indigenous nations, and the Martuwarra Fitzroy River Council was established in 2018 to oversee the cultural and environmental governance of the catchment. Paddlers should be aware of this context and any protocols established by Traditional Owners when planning trips.