Atrato, a river of Colombia, South America, rises near lat. 5° 20' N. and lon. 76° 50' W., and flows nearly due N. for about 250 m. to the gulf of Darien. The bar at its mouth being crossed, it has a wide channel not less than 35 ft. deep for the first 96 m., with a fall not exceeding 2 1/2 inches to the mile; and for 42 m. further a channel exceeding 18 ft. in depth can be cleared; while the distance across to the Pacific ocean, from which the river is separated by one of the lowest ranges of the Andes, does not exceed 50 m., and western branches of the Atrato are said to almost meet rivers from the Pacific having their source in this dividing ridge. Examinations have been made with the view of determining the practicability of constructing a ship canal by this river, to connect the Caribbean sea with the Pacific. The latest was by the United States government in 1871. The route which promised the least difficulty between the middle branch of the Atrato and the Jurador, emptying into the Pacific, would require 48 m. of canal; the height of the watershed, which must be excavated or tunnelled, being more than 500 ft. - The Atrato for nearly its whole length runs through a low swampy region, which is entirely overflowed by freshets.

Quibdo, on its upper course, is the only town of any consequence on the river. It is a miserable place of 1,500 inhabitants, mostly •blacks, with some Indians and a few whites. It is situated on several isolated hillocks of gravel and clay, in the midst of the swampy region which extends all around. The temperature of the region is close and sultry, and the rainy season continues all the year. Gold is found in fine dust in the bed and banks of the Atrato, at and above Quibdo, and also of the different branches of the river. Some portions of the country are described as highly auriferous. Above Quibdo the Atrato receives several branches, of which the Quito is the most important. Were it not for the incessant fluctuations of this stream, which within a tew hours frequently reduce it from its ordinary ample channel depth of 7 ft. or more to 5 or 6 ft. or even less, the Quito would present with the Atrato an uninterrupted steamboat thoroughfare of no less than 252 m. from the gulf of Darien. The Quito is wholly in the gold region, and its branches appear to lie in the richest portion of it.

The caoutchouc tree abounds.