A river that is flowing well, or you floating in or flowing with a river, can represent peace or contentment with life or surrender to a higher power.
Fighting against the current, trying to go upstream can represent trying to "go against the flow."
A dry riverbed can represent feeling your life is empty or not moving forward, or feeling unfulfilled.
A river overflowing its banks can represent feeling overwhelmed with a particular aspect of life, or possibly a feeling of abundance.