In the wetter south and southwest areas of Ghana, the river and stream pattern is denser, but in the area north of the Kwahu Plateau, the pattern is much more open, making access to water more difficult. Several streams and rivers also dry up or experience reduced flow during the dry seasons of the year, while flooding during the rainy seasons is common.
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 Cфte 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.
On the other side of the Kwahu Plateau from Lake Volta are several river systems, including the Pra, Ankobra, Tano and Densu. The Pra is the easternmost and the largest of the three principal rivers that drain the area south of the Volta divide. Rising south of the Kwahu Plateau and flowing southward, the Pra enters the Gulf of Guinea east of Takoradi. In the early part of the twentieth century, the Pra was used extensively to float timber to the coast for export. This trade is now carried by road and rail transportation.
The Ankobra, which flows to the west of the Pra, has a relatively small drainage basin. It rises in the hilly region of Bibiani and flows in a southerly direction to enter the gulf just west of Axim. Small craft can navigate approximately eighty kilometers inland from its mouth.
At one time, the Ankobra helped transport machinery to the gold-mining areas in the vicinity of Tarkwa. The Tano, which is the westernmost of the three rivers, rises near Techiman in the center of the country. It also flows in a southerly direction, but it empties into a lagoon in the southeast corner of Cфte d'Ivoire. Navigation by steam launch is possible on the southern sector of the Tano for about seventy kilometers.
A number of rivers are found to the east of the Pra. The two most important are the Densu and Ayensu, which are important as sources of water for Accra and Winneba, respectively. The country has one large natural lake, Lake Bosumtwi, located about thirty-two kilometers southeast of Kumasi.
It occupies the steep-sided caldera of a former volcano and has an area of about forty-seven square kilometers. A number of small streams flow into Lake Bosumtwi, but there is no drainage from it. Apart from providing an opportunity for fishing for local inhabitants, the lake serves as a tourist attraction.