The major drainage divide runs from the southwest part of the Akwapim-Togo Ranges northwest through the Kwahu Plateau and then irregularly westward to the Côte d'Ivoire border. Almost all the rivers and streams north of this divide form part of the Volta system. Extending about 1,600 kilometers in length and draining an area of about 388,000 square kilometers, of which about 158,000 square kilometers lie within Ghana, the Volta and its tributaries, such as the Afram River and the Oti River, drain more than twothirds of the country. To the south of the divide are several smaller, independent rivers. The most important of these are the Pra River, the Tano River, the Ankobra River, the Birim River, and the Densu River. With the exception of smaller streams that dry up in the dry seasons or rivers that empty into inland lakes, all the major rivers in the country flow into the Gulf of Guinea directly or as tributaries to other major rivers. The Ankobra and Tano are navigable for considerable distances in their lower reaches.
Navigation on the Volta River has changed significantly since 1964. Construction of the dam at Akosombo, about eighty kilometers upstream from the coast, created vast Lake Volta and the associated 768,000-kilowatt hydroelectric project. Arms of the lake extended into the lower-lying areas, forcing the relocation of 78,000 people to newly created townships on the lake's higher banks. The Black Volta River and the White Volta River flow separately into the lake. Before their confluence was submerged, the rivers came together in the middle of the country to form the main Volta River. The Oti River and the Daka River, the principal tributaries of the Volta in the eastern part of the country, and the Pru River, the Sene River, and the Afram River, major tributaries to the north of the Kawhu Plateau, also empty into flooded extensions of the lake in their river valleys. Lake Volta is a rich source of fish, and its potential as a source for irrigation is reflected in agricultural mechanization agreement signed in the late 1980s to irrigate the Afram Plains. The lake is navigable from Akosombo through Yeji in the middle of the country; a twenty-four-meter pontoon was commissioned in 1989 to link the Afram Plains to the west of the lake with the lower Volta region to the east. Hydroelectricity generated from Akosombo supplies Ghana, Togo, and Benin.