On the rivers, the banks are okay - but I would dry brush them to better blend them with the other terrain - at least the outer sides, maybe less so on the inner sides to get a bit of the mud look.
The river surface, for my tastes, is WAY too blue, though you did good by varying depth colors. Rivers tend to be more green than blue.
If you have easy access to acrylic gloss medium, get some - the higher the gloss the better. Mix a little green acrylic paint (not grass green and Definitely not bright green!) with the gloss and add it as a top layer, then a layer with a lighter muddy brown, and then another layer with more green in the gloss mix. Keep the mixes very opaque so lower layers still show through - and let them dry between coats or you will lose the desired effect.
And if the mood strikes, in the top couple of layers sparingly add some bits of glitter to give the river a bit of a sparkle.
As always, best to have a test piece to work on to make sure you like the results before you are fully committed.
One of the nice features of acrylic gloss medium is it is easy to clean and, if really needed, easy to add a top layer of plain gloss medium.