One of the larger tributaries of the Amazon, rises as the Guainia in SE. Columbia; crosses Venezuela and Brazil in a more or less SE. direction, and joins the Amazon (the Maranon here) near Manaos after a course of 1350 m.; some of its tributaries connect the Orinoco with the Amazon. 2, Has its source in a small lake in the Chilian Andes, flows NE. and E. to the Atlantic, is some 500 m. long, and easily navigated.