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 and the Salinas River, also known as the Rio Chixoy, or the Rio 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.

The Pasión River is a river located in the northern lowlands region of Guatemala. The 353.9-kilometre-long (219.9 mi) river is fed by a number of upstream tributaries whose sources lie in the hills of Alta Verapaz. These flow in a general northerly direction to form the Pasión, which then tends westwards to meet up with the Salinas River at 16°28′52″N 90°32′39″W. At this confluence, the greater Usumacinta River is formed, which runs northward to its eventual outlet in the Gulf of Mexico. The Pasión River's principal tributaries are the San Juan River, the Machaquila River, and the Cancuén River.