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.

At this confluence, the greater Usumacinta River is formed, which runs northward to its eventual outlet in the Gulf of Mexico.

The riverine drainage system of the Pasión and its tributaries covers an area of over 5,000 square kilometres (1,900 sq mi) and forms a watershed for a substantial portion of the present-day Guatemalan department of Petén's western half.

Maya ceremonial and urban centers located within the region include Dos Pilas, Tamarindito, Altar de Sacrificios, Aguateca, Seibal and Machaquila.

[5] Tranquilino Xojalaj, administrator of REPSA, declared that heavy rain caused the treatment wells to flood into the river,[6] however the company denied responsibility, stating that they do not use Malathion as a pesticide.