In the center-north of the country, the number of rivers that form valleys of agricultural importance increases. Noteworthy are the Elqui with 75 km long, 142 km Aconcagua, Maipo with 250 km and its tributary, the Mapocho with 110 km, and Maule with 240 km. Their waters mainly flow from Andean snowmelt in the summer and winter rains. The major lakes in this area are the artificial lake Rapel, the Colbun Maule lagoon and the lagoon of La Laja.