If you are swimming in a dream, such dream foretells about your emotions that are floating within. You are the person who does not initiate things by himself, instead you adapt to the present circumstances. The swimming is also a symbol of freedom. To swim underwater, means that you dispose other opinions and stay putted only with your own instincts.
Dream dictionary: swimming underwater dream meanings
If we dream that fishes are escaping from our hands when we try to get them out of the sea, then this reflects our emotional frustrations. Seeing fishes swimming between rocks or hiding underwater tells us about the desire of evading responsibilities that are a burden to us.