It has its headwaters in the Ecuadorian province of Cotapaxi, 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.