The Rio Grande ( or ; Spanish: Río Bravo del Norte, or simply Río Bravo) is one of the principal rivers (along with the Colorado River) in the southwest United States and northern Mexico. The Rio Grande begins in south-central Colorado in the United States and flows to the Gulf of Mexico. After passing through the length of New Mexico along the way, it forms part of the Mexico–United States border. According to the International Boundary and Water Commission, its total length was 1,896 miles (3,051 km) in the late 1980s, though course shifts occasionally result in length changes. Depending on how it is measured, the Rio Grande is either the fourth- or fifth-longest river system in North America.The river serves as part of the natural border between the U.S. state of Texas and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. A very short stretch of the river serves as part of the boundary between the U.S. states of Texas and New Mexico. Since the mid–20th century, heavy water consumption by farms and cities along with many large diversion dams on the river has left only 20% of its natural discharge to flow to the Gulf. Near the river's mouth, the heavily irrigated lower Rio Grande Valley is an important agricultural region.
The Rio Grande's watershed covers 182,200 square miles (472,000 km2). Many endorheic basins are situated within, or adjacent to, the Rio Grande's basin, and these are sometimes included in the river basin's total area, increasing its size to about 336,000 square miles (870,000 km2).