In geography, a confluence (also:  conflux) occurs where two or more watercourses join to form a single channel. A confluence can occur in several configurations:  at the point where a tributary joins a larger river (main stem); or where two streams meet to become the source of a river of a new name (such as the confluence of the Monongahela and Allegheny rivers at Pittsburgh, forming the Ohio); or where two separated channels of a river (forming a river island) rejoin at the downstream end.