w to animate water in river

here is a tutorial that might just help. A little old but gives you a good idea of how to move water in animate.

https://www.youtube.com/watch?v=-8w9HYXXP9M 

put each in it's own layer if you want them to have (even slightly) different movement (including speed).

then use a motion tween and adjust the paths.  to save time, you might want to create as handful of tile movieclips so you can reuse them instead of having to convert each tile into a movieclip while creating the tween.