The Colo River is a river in New South Wales, Australia. The Colo River begins at the confluence of the Wolgan River and the Capertee Rivers, north of Lithgow. The river flows eastwards and then south through a deep gorge in the northern Blue Mountains and ultimately ends at the point at which it flows into the Hawkesbury river at Lower Portland. The Colo River is approximately 97 klms in length.

The first 62klms of the Colo is inaccessible due to cliffs on either side of the river, except by experienced and hardy bushwalkers who brave the trackless scrub to experience a truly wild place less than 100klm from the CBD of Sydney. The lower part of the Colo (35 klms) is developed and has farms on either side of the river.

The Colo wilderness was saved from development, logging and damming, in the late 1970’s by the Colo Wilderness Preservation Society and other environmentalists. The Blue Mountains National Park area, including the Wollemi National Park, has received World Heritage listing, due in part to the discovery of the Wollemi Pine, often described as a ‘living fossil’ from the age of the dinosaurs.

The Colo River drains into the Hawkesbury River and then some 70 kms later out to sea. The Colo River is fresh water for its entire length but is tidal up to approximately 1.5 klms west of the Colo Bridge on the Putty Road. The tide at the Putty road bridge is approximately 4 hours behind that of Sydney Harbour at Fort Denison.

There is considerable community environmental activity through the Friends of Colo group and a number of riverbank management projects underway with private landholders. There are current efforts to rid the Colo of lantana which has taken hold in some of the lower parts of the river.