The San Juan River is the largest and most important river in the Mexican state of Nuevo León. The river feeds the El Cuchillo Dam, which provides the city of Monterrey with water. The San Juan River basin has a total surface area of 33538 km2. The San Juan River is a tributary to the Rio Grande (Rio Bravo) — which is the fourth largest river basin in North America. It begins in Coahuila, flows through Nuevo León and into Tamaulipas, where it finally joins the Rio Grande near Camargo, Tamaulipas.