|Native name||Río Pastaza (Spanish)|
|• elevation||4,570 m (14,990 ft)|
|120 m (390 ft)|
|Length||710 km (440 mi)|
|Basin size||39,504 km2 (15,253 sq mi)|
|• location||Confluence of Marañón (near mouth)|
|• average||2,769 m3/s (97,800 cu ft/s)|
|Official name||Complejo de humedales del Abanico del río Pastaza|
|Designated||5 June 2002|
The Pastaza River (Spanish: Río Pastaza, formerly known as the Sumatara) is a large tributary to the Marañón River in the northwestern Amazon Basin of South America.
It has its headwaters in the Ecuadorian province of Cotopaxi, flowing off the northwestern slopes of the volcano Cotopaxi and known as the Patate River. The Patate flows south and in Tungurahua Province it is joined by the Chambo River just upstream from the town of Baños de Agua Santa just north of the volcano Mount Tungurahua and becomes the Pastaza. Seven kilometers east of Baños, it is dammed for the Agoyán hydroelectric project, which has created a silty lagoon by the village of La Cieniga. The Agoyán dam was placed in that location specifically to leave the famous Falls of Agoyán, about 5 km further downstream, intact. After the waterfall the river enters a gorge where there is very fast whitewater with class-4 rapids; it is often used for whitewater rafting although it is not considered to be of the same quality as the Tena River and is therefore less popular for the sport.
From the junction with the Chambo, the Pastaza flows almost due east for about 275 kilometres (171 mi) where it then turns south-east, as it is joined by the Topo River. The Troncal Amazonas highway parallels the river from Baños to Puyo, passing through seven tunnels, and four major waterfalls that are touristic destinations for many Ecuadorians (Agoyán and Pailón del Diablo being the most popular.) Just past the town of Santa Inez, the Pastaza River crosses into the province of Pastaza, where it forms the boundary between that province and Morona-Santiago. At the town of Mera, shortly before reaching Puyo, the river exits the mountains and flows into a wide valley, becoming wider and shallower. After Shell the river becomes braided and meanders, leaving oxbows and sloughs along its route across the Amazonian floodplain.
After cutting through Ecuador, the Pastaza passes into Peru at the village of Hito Zoilaluz on Isla Zoilaluz and flows south into the Marañón River near Puerto Industrial.