I agree. Since the landmass is already green, I'd just darken the area around them a bit to indicate the river valleys.

I think you overused one of your mountain symbols: the one with the large mountain and a smaller one attached to its right side. It's a distinctive arrangement, so it stands out that you used it a lot. The triple peak with a large mountain in front and two tucked in behind it drew my attention, also; you used it quite a bit, too.