Spanish  Río Abuná,  Portuguese  Rio Abunã,  headwater of the Amazon, rising in several streams, east of the Cordillera Oriental of the Andes. The navigable river flows for about 200 miles (320 km) northeast through rain forests, forming Bolivia's northern border with Brazil. It joins the Río Madeira, a tributary of the Amazon, at Manoa, Bolivia. Rubber, Brazil nuts, quinine, and other forest products are the principal items of commerce in the sparsely inhabited Abuná region.