Lagunas de Chacahua National Park in the context of Herons

The Atoyac River is a river in Oaxaca, Mexico. The Atoyac flows into the Rio Verde which empties into the Pacific near Laguna Chacahua, in Lagunas de Chacahua National Park, 90 km west of Puerto Escondido. The mountainous terrain of the region it occupies allows for no navigable rivers; instead, there are a large number of smaller ones, which often change name from area to area. The continental divide passes through the state, meaning that there is drainage towards both the Gulf of Mexico and the Pacific Ocean. Most of the drainage towards the Gulf is represented by the Papaloapan and Coatzacoalcos Rivers and their tributaries such as the Grande and Salado Rivers. Three rivers account for most of the water headed for the Pacific: the Mixteco River, Tehuantepec River, and the Atoyac, with their tributaries.

During 1984's Hurricane Odile, eighteen passengers and three crewman drowned in flooding on the Atoyac River.

The Río Verde is a river in the state of Oaxaca in Mexico. It is formed by the confluence of the Atoyaquillo and Colorado Rivers near the village of Santiago Ixtayutla and flows south to its mouth at El Azufre on the Pacific Ocean, on the western border of Lagunas de Chacahua National Park. Its major tributary is the Atoyac, which drains the Oaxaca Valley and flows into the Río Verde at Paso de la Reina, where a proposal to build a large hydroelectric dam project has been opposed by local communities. The combined length of the Atoyac and lower Verde rivers is 342 kilometres (213 mi) and the river system as a whole drains a watershed of 18,812 square kilometres (7,263 sq mi), which has a mean natural surface runoff of 6,046 hm (2.135×10 cu ft) per year. The watershed covers almost a fifth of Oaxaca state and is home to over a third of its population, and faces serious degradation issues as a result of pollution and overexploitation.

Well-studied Mesoamerican civilizations flourished in the valleys of Oaxaca, Ejutla and Nochixtlán, all of which lie in the Verde–Atoyac basin. The floodplains of the lower Río Verde valley also began to support large populations and complex society in the Late Formative period (400–100 BC). The site of Río Viejo emerged as a regional centre during the Miniyua phase (150 BC–100 AD), developing massive public architecture by the Late Classic period (550–800 AD). In the Postclassic period development shifted away from the floodplains to the city-state of Tututepec, located in the foothills about 16 km east of Río Viejo.