You probably just need to make a sprite animation. Ideally, the animated elements are separate from the still background. You simply make a game object, plug the animation component onto it, import the sprite sheet and then drag the different sprites onto the timeline in the animation window. The procedure is the same for when the entire background has animation frames. If you’ve never done this, look up beginner tutorials on sprite animation.
Also note, when the animation is a transform, i.e. an object or waterlevel just moves up and down, a wheel spins, etc, you are better off with using keyframes. This is also quite basic and the best is to watch introduction tutorials on YouTube.