Usumacinta River

The Usumacinta River is a river in southeastern Mexico and northwestern Guatemala. It is formed by the junction of the Pasión River, which arises in the Sierra de Santa Cruz (in Guatemala) and the Salinas River, also known as the Chixoy, or the Negro, which descends from the Sierra Madre de Guatemala. It defines part of the border between Guatemala and the Mexican state of Chiapas, then continues its northwesterly course, meandering through the Mexican state of Tabasco to the Gulf of Mexico.

After serving as a border between Mexico and Guatemala, the Usumacinta River enters Mexican territory in the state of Tabasco and across the Usumacinta Canyon ecological reserve, forming impressive canyons along its route. Passing the canyon called "Boca del Cerro", Tenosique, the Usumacinta goes into the plain of Tabasco.

In Tabasco, the Grijalva River flows in to the Usumacinta River. This confluence is located at Tres Brazos, Centla, and it forms a large wetland region known as the Wetlands of Centla. The Wetlands of Centla is also the name of a biosphere reserve in the area; it contains 302,702 hectares, which makes it the largest protected wetland region in North and Central America and one of the top 15 wetlands (by size) in the world.

The total length of the river, including the Salinas, Chixoy, Negro rivers in Guatemala is approximately 1,000 km (620 mi). It is the only visible natural boundary separating the Yucatán Peninsula from Mexico.