According to the International Boundary and Water Commission, the Rio Grande River starts in the San Juan Mountains in Colorado and continues 1,901 miles to the Gulf of Mexico. It is among the 20 longest rivers in the world and is the fifth-longest in the United States.
The Rio Grande River forms a 1,255-mile-long border segment between Mexico and the United States. The Rio Grande and Rio Bravo watershed in its entirety encompass approximately 335,000 square miles, with 50,000 of those square miles lying within that state of Texas. Approximately half of the entire watershed is in Mexico, and half lies within the United States.