San Juan Bautista Tuxtepec in the context of Papaloapan Region

The Papaloapan River (Spanish: Río Papaloapan) is one of the main rivers of the Mexican state of Veracruz. Its name comes from the Nahuatl papaloapan meaning "river of the butterflies".

In 1518 Juan de Grijalva's expedition spotted the river, naming it Río de Alvarado. The Papaloapan rises in the Sierra Madre de Oaxaca on the border between the states of Veracruz and Oaxaca. It is formed where the Santo Domingo River and the Valle Nacional River join to the southwest of San Juan Bautista Tuxtepec in Oaxaca. The Tonto River is another major tributary.The Papaloapan meanders for 122 km (76 mi) in a northeasterly direction through the coastal plain before draining into Alvarado Lagoon.The river basin covers 46,517 km (17,960 sq mi), the second largest in Mexico, and contains 244 municipalities with a population of about 3.3 million people.The cities of San Juan Bautista Tuxtepec and Tlacotalpan (Veracruz) are situated on the banks of the Papaloapan.

The Santo Domingo River, in the Mexican state of Oaxaca, is one of the main tributaries of the Papaloapan River. It is formed by the confluence of the Salado and Grande rivers, which drain the dry Tehuacán and Cuicatlán valleys west of the Sierra Madre de Oaxaca. The Santo Domingo river flows east through the Sierra Madre, dividing the Sierra Zongolica sub-range to the north from the Sierra Juárez to the south. It joins with the Valle Nacional River above San Juan Bautista Tuxtepec to form the Papaloapan.

Carrying sediment from the mountains, it was a major cause of flooding in the coastal plain of Veracruz by reducing the capacity of the Papaloapan to drain the plains.To alleviate these problems, the Cerro de Oro Dam was constructed on the river just above the junction with the Valle Nacional, completed in 1989. The reservoir behind the dam is connected by a channel to Lake Miguel Alemán, the reservoir formed by the Miguel Alemán Dam on the Tonto River.

The Valle Nacional River is a river of Oaxaca state in Mexico.The river originates in the Sierra Juárez.The ecology of the region, originally one of pine forests, is threatened by logging, agriculture and grazing.The Valle Nacional flows past San Juan Bautista Valle Nacional, and joins the Santo Domingo River to the southwest of San Juan Bautista Tuxtepec to form the Papaloapan River.

The Tonto River is a river of Oaxaca, Mexico that flows from the mountains of Zongolica. It is dammed by the Miguel Alemán Dam near the town of Temascal or Nuevo Soyaltepec, forming the Miguel Alemán Lake.Below the dam, the river flows southeast past San Juan Bautista Tuxtepec, where it joins the Santo Domingo River to form the Papaloapan River.