Rivers often mix; allowing their waters  to meet and mingle and swirl and be one,
Often rivers split however, after years of a certain current on one odd angle could bore its way into a body of land and once again these rivers would separate, only to meet again in whatever reservoir they may drain into which is intermittently connected with every other natural water source, ultimately reuniting with other waters including their own;
Along the way though some take their time. they meander lazily flowing more directions than they could ever practically need to but I think they do it because those other rivers take the whole punctuality thing too seriously, and either way theyre already there.