An object in this meaning is the same thing as an objective[?] or task[?]. It comes from old project terminology and refers to the act of actually performing something according to a plan, or rather "according to a project" (the word "project" used to mean "plan").
... volume, the Parana[?] with its impressive Iguaçu[?] falls, the Rio Negro, São Francisco[?], Xingu, Madeira and the Tapajós[?] rivers.
Situated along the equator, ...