The Colorado River (Spanish: Río Colorado) is a river in the south of Argentina. It has its sources on the eastern slopes of the Andes in the latitude of the Chilean volcano Tinguiririca (about 34° 48' S.), and pursues a general east-southeast course to the Atlantic Ocean, where it discharges through several channels of a delta extending from latitude 39° 30' to 39° 50' S. Its total length is about 620 miles, of which about 200 miles from the coast up to Pichemahuida is navigable for vessels of 7 ft. draft.

This river has been usually described as being formed by the confluence of the Grande and Barrancas, but as the latter is only a small stream compared with the Grande it is better described as a tributary, and the Grande as a part of the main river under another name. After leaving the vicinity of the Andes, the Colorado flows through a barren, arid territory and receives no tributary of note except the Curaco, which has its sources in the Pampas, and is considered to be part of the ancient outlet of the now closed lacustrine basin of southern Mendoza. The bottom lands of the Colorado in its course across Patagonia are fertile and wooded, but their area is too limited to support more than a small, scattered population.