I like what you did in the center forest with the river being obscured by the trees. That being said each of your river systems have strange branches that don't seem to make sense. Water always flows downhill so look at each arm and ask yourself if it looks like it's coming from a high elevation area. If it doesn't you need to redraw the river or add some elevation in to make things make sense. There is a stickied tutorial in the tutorial forum that goes over all of the rules to drawing river systems, you should give it a read.