The only instances I know of rivers naturally splitting is in river deltas. These form from sediment accumulating at what was once a single river mouth. The isl

The only instances I know of rivers naturally splitting is in river deltas. These form from sediment accumulating at what was once a single river mouth. The islands in a delta have consistent properties: they are flat, consist of soil and silt rather than rock, and are usually marshy. Anything that deviates from these rules is usually wrong. Rivers don't split around two sides of a mountain, for example.