The New River 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. The river as known today formed from a levee failure and massive flooding that filled the Salton Sea.
The river flow mostly consists of agricultural runoff, municipal discharge and industrial wastewater. The river has been called the most severely polluted river of its size in the United States. Several projects have begun to reduce and mitigate the levels of pollution in the river, including upgrades to sewage treatment infrastructure and enclosure of the river channel.