I know nothing about the location. However, I would assume that these paths are not natural but to some extent man made. With dams, locks, gates, channeling, etc., one can make water do almost anything. It usually keeps doing it as long as these channeling structures are maintained. Once they fall apart, the water usually starts reverting back to a natural path, although not necessarily the original path. Here in Europe, the Rhine-Main-Danube canal even flows across watersheds. Ditto for the canal that cuts Scotland in two, going up from one coast and then back down to another.
But remember please: I am not a member of the river police!