Loa River, Spanish Río Loa, river, the northern Chile. The longest river in Chile, in Antofagasta and Tarapacá regions. It it rises in the Andes at the base of Miño Volcano, near the Bolivian border, and flows southwest through the mountains, emerging at the oasis of Calama; it then veers westward and northward across the Atacama Desert. About 45 miles (70 km) north of Tocopilla it turns westward again, crosses the coastal mountain range, and empties into the Pacific Ocean after a course of 275 miles (about 440 km). Although it is not navigableBefore it receives the runoff of the Saládo River, its waters irrigate Calama and other oases, provide Antofagasta region with drinking water, and are used to generate hydroelectric power for nearby copper and nitrate mines.