The Cauca River is a river in Colombia that lies between the Occidental and Central cordilleras. Born in southwestern Colombia near the city of Popayán, it joins the Magdalena River just south of Santa Cruz de Mompox. It has a total length of 1350 km. from origin to mouth. The river is under the supervision of the Corporación Regional del Cauca and the Corporación Autonoma Regional del Valle del Cauca.
On November 18, 2007 Colombian newspaper El Tiempo reported that the river was receiving an average of 500 tons of residual waters a day. Pollution from the city of Popayan, seven gold mines that also add industrial pollutants such as mercury, some 8 sand mills, plus a couple of mines of coal and bauxite. Cali, the largest city over the river depends on the river in a 76%. Adding to these other affluent rivers collect residual waters from other major cities and deposit an aproximate of 330 tons of residual waste into the river, by the time it gets to Yumbo the river has no oxygen.