What is the only river that crosses the equator twice?

The Congo River, formerly known as the Zaire River under the Mobutu regime, is the second longest river in Africa, shorter than the Nile, as well as the second largest river in the world by discharge volume, following only the Amazon. It is also the world's deepest recorded river, with measured depths in excess of 220 m (720 ft). The Congo-Lualaba-Chambeshi River system has an overall length of 4,700 km (2,920 mi), which makes it the world's ninth-longest river. The Chambeshi is a tributary of the Lualaba River, and Lualaba is the name of the Congo River upstream of Boyoma Falls, extending for 1,800 km (1,120 mi).

Measured along with the Lualaba, the main tributary, the Congo River has a total length of 4,370 km (2,715 mi). It is the only river to cross the equator twice. The Congo Basin has a total area of about 4,000,000 km2 (1,500,000 sq mi), or 13% of the entire African landmass. Not until it crosses the equator will it at its last turn, turns away from this course and, taking a remarkable counter-clockwise arc first to the west and then to the southwest, then flow back across the equator and on down to the Atlantic. In this the Congo is exceptional. No other major river in the world crosses the equator even once, let alone twice.

The river and its tributaries flow through the Congo Rainforest, the second largest rain forest area in the world, second only to the Amazon Rainforest in South America.