What is "purus"

Usage examples of "purus".

It additionally mentions that nineteenth-century rubber traders plied the Negro, the Madeira, and the Purus, that the "finest quality of india-rubber comes from the Acre and Beni districts of Bolivia, especially from the valley of the Acre (or Aquiry) branch of the river Purus," and that 35% of the Amazon Basin rubber is from the province of Para.