Brazos (brăzˈəs) [key], river, 870 mi (1,410 km) long (1,210 mi/1,947 km long with its main tributary), rising in E N.Mex. From its source it flows SE across Texas to enter the Gulf of Mexico at Freeport. The Brazos flows through a fertile farming area of N Texas, where cotton is produced in the irrigated river's valley. The Brazos supplies water to nearby cities; several dams provide flood control and hydroelectric power. The river is navigable upstream.