Those areas have formed by a succession of deltas that overlap each other and slowly subside. The extremely tattered look of the Mississippi delta is due in large part to canalization of the main river channel and loss of new sediments over the continental shelf edge. The old sediments are subsiding, leaving just the natural levees and the man-made road systems.

As Ascension pointed out, your channels are much too large compared to the incoming river. The active delta regions should have distributaries (the split-apart end of the river) that carry as much water as the incoming river. Those channels would have to be extremely shallow and the incoming one extremely deep to get the effect that you have there. A delta forms where a river slows down dramatically and drops sediment. This slowdown can be due to a sudden change in the slope of the land (your typical alluvial fan or the Okavongo Delta in Africa) or where a river enters a very flat body of water such as a lake or the ocean. If the land is relatively flat and the river's sediments are in steady-state between erosion and deposition, the river will expend its energy cutting side-to-side, forming meanders.

The colors look reasonable, though. One thing to watch out for on the Nile delta coloration is that it's pretty much all farmland that's giving it that bright green color. There aren't too many wild deltas left that are above water. The main reason that the Mississippi delta wasn't overly farmed is that it was a bit too swampy. However, those strips of farmland on either side of the river show that people did what thye could to farm it.

It's hard to say too much without a scale, though.