A tributary is a river or stream that flows into a larger river. One of the tributaries of the Amazon River is the Ucalayi, which joins the Amazon in Peru.
One of the tributaries of the Ucalayi is the Apurimac. This river rises in the mountains of Peru, about 120 miles from the Pacific Ocean.
It’s possible, then, to follow the Apurimac, Ucalayi, and Amazon rivers from within a short distance of the Pacific all the way to the Atlantic Ocean, across almost an entire continent!