You should take a look at C2's autorunner example. Just open up C2, select new, then scroll down to autorunner. It creates platforms and moves them across the screen, as you mention in your title!
You'd need to do a bit of tinkering, but it should give you a good starting point for what you want!
With regard to the river, you could just make it part of your background layer. There are some really good water effect examples posted on the forum (here for example). Just type water effect into the search box and you're bound to find something useful.
Good luck! :)