The New River (Río Nuevo in Spanish) flows north from near Cerro Prieto, through the city of Mexicali, Baja California, Mexico, into the United States through the city of Calexico, California, towards the Salton Sea. The river channel has existed since pre-historic times; however, the river as known today was formed from a levee failure that resulted in massive flooding that re-created the Salton Sea. Today, the river flow is not natural, mostly consisting of agricultural runoff, municipal discharge and industrial dumping. The river has been referred to as the most severely polluted river of its size within the United States.