Two things jump out about the rivers - they are very blue and very even - more like a canal. A natural river isn't of equal width all along its course. If you varied the sides more it would appear more natural looking.
Hi Jon-1066
I know they are blue tried to get them a greenish brown but failed in my attempts so through frustration I went blue and got it done.
I did not have the facilities to make curvy sections only had the ability to design straight and circular sections hence the number of more smaller straights with more turns to get the curvy look. They were laser cut for curvy sections I would have to cut by hand, to much work for me there.