71% of earth mass according to widespread although apparently unproven belief appears to be much heavier than a bird and to the best of my knowledge water doesn't have wings so it can't fly freely at ease. So probability calculations leads to the conclusion that flying birds are much more likely to occur in nature than flying water.

I do believe that birds fly because they have never heard about Theory of Gravity while humans do not fly because they are gullible and tend to believe in many unproven theories.