The Rio Grande ( or ; , or simply Río Bravo) is one of the principal rivers in the southwest United States and northern Mexico (the other being the Colorado River). The Rio Grande rises from south-central Colorado in the United States and flows to the Gulf of 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 in the late 1980s, though course shifts occasionally result in length changes. Depending on how it is measured, the Rio Grande is the fourth- or fifth-longest river system in North America.