By the way, I found a small bug. The enemies explode when they have contact with each other. But if one collide with another one which just spawned on the edge before it got released, then the one on the edge does not explode, it only disappears after a short time.

3464 30xx (forgot) Tricky, but not impossible (yet). ;)

Sometimes the river still does look quite ugly, but much better than this diagonally river :D Actually it looks good! Maybe you could make the river not touching the river again, so it does not loop or create some other unrealistic figures like flowing back, but I am not really sure if that is possible/"easy" to implement. Maybe worth a try. And then, get the units working =)