The second comprises the tributaries of the Amazon River in the montaña region. In the third the principal feature is Lake Titicaca, which drains into Lake Poopó in Bolivia through the Desaguadero River.

The Napo, Tigre, and Pastaza rivers rise in Ecuador and flow into Peru. The latter two streams are tributaries of the Marañón River, and the Napo empties into the Amazon River. The border between Peru and Colombia is delineated by the Putumayo River. Encarta