Pilcomayo (in Hispanicized spelling) (Quechua Pillkumayu or Pillku Mayu, pillku red, mayu river, "red river", Guarani Ysyry Araguay Guaraní: [ʔɨsɨˈɾɨ ʔaɾaɰʷaˈɨ]) is a river in central South America. At long, it is the longest western tributary of the Paraguay River. Its drainage basin is in area, and its mean discharge is . Along its course, the Pilcomayo silts up and splits into two main branches, North and South. After some distance, these branches rejoin to form the Lower Pilcomayo. The Pil…