ATRATO, a river of western Colombia, South America, rising on the slopes of the Western Cordilleras, in 5° 36' N.
The Atrato at one time attracted considerable attention as a feasible route for a trans-isthmian canal, which, it was estimated, could be excavated at a cost of ii,000,000.
If the line which formerly separated the Colombian departments of Cauca and Panama is taken as forming the international boundary, this line follows the water-parting between the streams which flow eastward to the Atrato, and those which flow westward to the Gulf of San Miguel, the terminal points being near Cape Tiburon on the Caribbean coast, and at about 7° so' N.
A small part of the northern Colombia, on the lower courses of the Atrato and Magdalena, extending across the country from the Eastern to the Western Cordilleras with a varying width of 100 to 150 m., not including the lower river basins which penetrate much farther inland, also consists of low, alluvial plains, partly covered with swamps and intricate watercourses, densely overgrown with vegetation, but in places admirably adapted to different kinds of tropical agriculture.
The Western Cordillera branches from the main range first and follows the coast very closely as far north as the 4th parallel, where the San Juan and Atrato rivers, thoughflowing in opposite directions and separated near the 5th parallel by a low transverse ridge, combine to interpose valleys between it and the Cordillera de Baudo, which thereafter becomes the true coast range.
It then forms the divide between the Cauca and Atrato valleys, and terminates near the Caribbean coast.
It divides on the Panama frontier, the easterly branch forming the watershed between the Atrato and the rivers of eastern Panama, and serving as the frontier between the two republics.
The San Juan is distinguished for having been one of the proposed routes for a ship canal between the Caribbean and Pacific. At one point in its upper course it is so near the Atrato that, according to a survey by Captain C. S.
The rivers belonging to the Caribbean system, all of which flow in a northerly direction, are the Atrato, Bacuba, Sinu, Magdalena and Zulia.
Like the Atrato it brings down much silt, which is rapidly filling that depression.
It receives the waters of the Atrato, Bacuba, and a number of small rivers, and penetrates the land about 50 m., but has very little commercial importance because of the unhealthy and unsettled character of the neighbouring country, and because of the bar across its entrance formed by silt from the Atrato.
The rainfall on this coast is said to average 73 in., though it is much higher at certain points and in the Atrato Valley.
The "manatee" (Manatus americanus) is found in the Atrato and other large Colombian rivers.
Another palm of much economic importance in Colombia is the "tagua" (Phytelephas macrocarpa),which grows abundantly in the valleys of the Magdalena, Atrato and Patia, and produces a large melon-shaped fruit in which are found the extremely hard, fine-grained nuts or seeds known in the commercial world as vegetable ivory.
Among the tribes which are still living in a savage state are the Mesayas, Caquetas, Mocoas, Amarizanos, Guipanabis and Andaquies of the unsettled eastern territories; the Goajiros, Motilones, Guainetas, and Cocinas of the Rio Hacha, Upar and Santa Marta districts; and the Dariens, Cunacunas, and Chocos of the Atrato basin.