A river of central Africa flowing about 4,666 km (2,900 mi) north, west, and southwest through the Democratic Republic of the Congo (formerly Zaire) to the Atlantic Ocean. Its remotest tributaries rise in northern Zambia. For much of its latter course the river forms the border between the Democratic Republic of the Congo and the Republic of the Congo. or Zaire River River, west-central Africa. Rising in Zambia as the Chambeshi and flowing 2,900 mi (4,700 km) through the Democratic Republic of the Congo to the Atlantic Ocean, it is the second longest river in Africa. It flows through three contrasting regions: the upper Congo, characterized by lakes, waterfalls, and rapids; the middle Congo, with seven cataracts known as Boyoma (Stanley) Falls; and the lower Congo, which divides into two branches forming a vast lake area called the Malebo (Stanley) Pool