Which river is the longest running entirely in Brazilian territory?

The São Francisco River is the longest river running entirely within Brazilian territory.

Known in Brazil as the Velho Chico, the river is about 2,830–2,914 kilometres long, depending on the measurement used. It rises in the Canastra Mountains of Minas Gerais, flows north through Minas Gerais and Bahia, then turns east toward the Atlantic Ocean.

The river crosses or borders five Brazilian states: Minas Gerais, Bahia, Pernambuco, Alagoas and Sergipe. That entirely national course distinguishes it from longer Brazilian rivers such as the Amazon, Paraná and Madeira, which cross international boundaries or form part of transnational systems.

The São Francisco is often called Brazil’s “river of national integration” because it links the Southeast and Northeast and remains vital in a semi-arid region. It supports irrigation, transport and hydroelectric power. Its mouth lies near the Alagoas–Sergipe border, and its basin includes tributaries from Goiás and the Federal District.