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Pilcomayo(pēlkōmä`yō), river c.1,000 mi (1,600 km) long, rising in the Bolivian Andes E of Lake Poopó and flowing SE in a marshy course across the Gran Chaco to the Paraguay River near Asunción. It forms part of the Argentina-Paraguay border.
a river in South America, a right tributary of the Paraguay River. The Pilcomayo is 1,200 km long and drains an area of 160,000 sq km. Rising in the Central Andes of Bolivia, it cuts through the Cordillera Oriental and flows out onto the Gran Chaco, where it forms the border between Argentina and Paraguay. The Pilcomayo becomes extremely shallow in winter; in summer (January-April) it overflows and submerges a wide band of land. The mean flow rate in the middle course is 167 cu m per sec. There is a hydroelectric power station on the upper course. The city of Asunción is at the river’s mouth.