Narrow in the highlands, the majority of the rivers broaden as they reach the lower elevations of the Coast and Oriente. During the rainy season, which lasts from January to April, the rivers that drain into the Pacific flood and often cause damage.
The two main water systems are the Esmeraldas River in the North and the Guayas in the South.
The Esmeraldas begins as the Guayllabamba River in the Sierra, flowing west before emptying in the Pacific near the city of Esmeraldas.
The Guayas forms to the north of Guayaquil, where the Daule and the Babahoyo Rivers converge. The Babahayo arises from its tributaries in the Andes. The Guayas basin covers 40,000 square kilometers.
The most important rivers in the Oriente are the Pastaza, Napo, and Putumayo. The Pastaza includes the Agoyan Waterfall, Ecuador's highest.