Two of Mexico's major rivers begin in the state of Colorado: the Rio Bravo, which is known as the Rio Grande north of the border, and the Colorado River. The Colorado River lies mainly in Colorado and flows southward, crossing the border into northwestern Mexico, where it empties into the Sea of Cortez, also known as the Gulf of California. The Rio Bravo, which forms about 1,250 miles of the border between Mexico and the U.S., will occasionally shift its position through flooding, therebycausing border disputes.
The Grijalva-Usumacinto is the Mexican river with the greatest amount of flow and, like the Rio Bravo and Colorado, begins outside of the country. This river system originates in Guatemala and has a double name because it consists of two branches of similar length. The two branches join in the southeastern Mexican state of Tabasco before emptying into the Gulf of Mexico.
The longest river, which lies entirely within Mexico and runs about 800 miles, is the Lerma-Santiago river system. It begins as the Lerma River, then flows into Lake Chapala and finally makes its way to the Pacific Ocean as the Santiago River. The Lerma-Santiago is considered one of the most important rivers in Mexico because of its value to the nation's economy. It flows through several of Mexico's states and provides water to prime agricultural lands.