I do not know if it's done on purpose but when we swim on the surface There is no animation of swimming and when we try to go up to the surface while swimming (Ctrl)
It bug a lot and sometimes we can not even breathe on the surface
  for that we must stop swimming and maintain the space key but I find it buggy enough and not natural.

Sorry my english is not good.

bug : https://youtu.be/9vR1oMDuf_Y

a first-person vision like that would be great: https://youtu.be/Ok7h94Hjl9Y

Thank you for your patience.