Torrential rivers on the slopes of the Andes mountains produce a large hydroelectric power potential and add their volume to the navigable rivers in the valleys. In the late 1980s, approximately 78 percent of the country's population lived in the Andean highlands.

The Río Cauca rises within 200 kilometers of the border with Ecuador and flows through some of the best farmland in the country. After the two cordilleras converge, the Cauca Valley becomes a deep gorge all the way to the Caribbean lowlands.

Between the Cordillera Central and the Cordillera Oriental flows the Río Magdalena. This 1,600-kilometer-long river rises near a point some 180 kilometers north of the border with Ecuador, where the Cordillera Oriental and the Cordillera Central diverge. Its spacious drainage area is fed by numerous mountain torrents originating high in the snowfields. The Río Magdalena is generally navigable from the Caribbean Sea as far as the town of Neiva, deep in the interior, but is interrupted midway by rapids. The valley floor is very deep; nearly 800 kilometers from the river's mouth the elevation is no more than about 300 meters.

The Caribbean lowlands region is in roughly the shape of a triangle, the longest side of which is the coastline. Most of the country's commerce moves through Cartagena, Barranquilla, Santa Marta, and the other ports located along this important coast. Inland from these cities are swamps, hidden streams, and shallow lakes that support banana and cotton plantations, countless small farms, and, in higher places, cattle ranches.

The Caribbean region merges into and is connected with the Andean highlands through the two great river valleys. After the Andean highlands, it is the second most important region in economic activity. Approximately 17 percent of the country's population lived in this region in the late 1980s.

The Pacific lowlands are a region of jungle and swamp. Most of the streams flow westward to the Pacific, but the largest, the navigable Río Atrato, flows northward to the Golfo de Urabá, making the river settlements accessible to the major Atlantic ports and commercially related primarily to the Caribbean lowlands hinterland.