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Içá(ēsä`), river, c.1,000 mi (1,600 km) long, rising in the Andes, S Colombia, and flowing SE to the Amazon in NW Brazil. Mostly navigable, it marks part of Colombia's boundary with Ecuador and most of Colombia's frontier with Peru. The river valley, once a major source of rubber, has declined somewhat in economic importance, but rubber and balatá are shipped to Manaus, Brazil. In the early 20th cent., during the peak of the wild-rubber bonanza, Roger Casement, a British consul, was appointed to head a group to investigate the treatment of Native American laborers in the region and made a report for the Peruvian government on the brutal exploitation of native labor; the report shocked the world.
a river in South America, a left tributary of the Amazon. The upper Putumayo forms the border between Colombia and Ecuador, and the middle Putumayo forms the border between Colombia and Peru. In its lower course the river flows through Brazil, where it is called the Içá. The Putumayo is 1,580 km long and drains an area of 123,000 sq km. It originates in the southern Andes of Colombia and flows primarily through the humid equatorial forests of the Amazon Basin. The mean annual flow rate of the Putumayo is 7,160 cu m per sec. The river is fed by rain. High water is from April through July. The lower course of the Putumayo is navigable.