Dreaming about water and things related to this element are usually positive dreams. Not just beautiful, waterfalls are also wonderful to interact with.
Dreaming about a waterfall may be reflective of the current state you are in and it all depends on the state of the water. If the water was cold, means that you better be careful who you share your weakness with. If it was fierce and powerful, means that you are happy and have tremendous courage. If the water was calm and clear, then it represents revitalization, regeneration and renewal.
To dream that you are swimming on a waterfall suggests that you are feeling emotionally overwhelmed.