Originating in the Colombian Andes near the town of Puracé, the river flows northward for about 600 miles before merging with the Magdalena River, eventually draining into the Caribbean Sea. As it descends from the Andes, the Cauca River enters the Valle del Cauca, a broad, fertile valley that is one of Colombia's most important agricultural regions. Here, the river flows through major cities like Popayán and Cali, providing essential water resources for irrigation and daily use. The river is very polluted and sections are considered "dead zones," where oxygen levels are too low to support most life forms.