Here's a shot from the bridge showing these two rivers coming together. Rivers in the tropics serve many purposes, from the obvious water source, to transportation, food procurement for any number of creatures including humans through fishing, etc. We ate plenty of locally caught fish while in the area. As naturalists, we find them interesting also because rivers create the natural demarkation for the geographic boundaries of many species of insects, birds and mammals alike. Understanding biogeography and species distribution in the tropics really involves careful consideration of the boudaries created by river systems historically and throughout the prehistory of an area, as much as can be determined.