The Colo River is a wild and remote waterway in New South Wales, rising on the Great Dividing Range northeast of Newnes where the Wolgan River and Capertee River converge. From its headwaters at approximately 218 metres elevation, the river descends 214 metres over its 86-kilometre course, flowing eastward and then south through a dramatic deep gorge within Wollemi National Park before emerging into a scenic, narrow agricultural valley and ultimately joining the Hawkesbury River near Lower Portland, north of Windsor. The catchment is entirely undeveloped — no towns, farms, or roads penetrate the wilderness interior — making the Colo one of the most pristine river systems within striking distance of Sydney, sitting just 70 kilometres from the city's geographical centre. The lower reaches transition to tidal and brackish water, supporting a different suite of species than the upper gorge country. The river is too shallow for conventional boats throughout much of its length, with extensive shallow sandbars defining its character, though canoes and kayaks can navigate it with effort.