The Coatzacoalcos is a large river that feeds mainly the south part of the state of Veracruz; it originates in the Sierra de Niltepec and crosses the state of Oaxaca in the region of the Isthmus of Tehuantepec, flowing for 325 kilometers [http://www.bartleby.com/69/36/C08836.html Coatzacoalcos River.