São Francisco River, a major river in eastern Brazil, the longest entirely within the country. It begins in southern Minas Gerais state and flows northeastward for most of its 1,800-mile (2,900-km) course, entering the Atlantic Ocean. River vessels can travel its middle course, but are prevented from reaching the sea by a series of rapids and falls. The river is used for irrigation, and the falls and several dams are used to generate hydroelectric power for a wide area of northeastern Brazil.