I have seen numerous posts regarding the clear view of the seabed when floating at surface level and slightly tilting your view downwards, so this post will not include a suggestion to fix that (although I hope those will be voted up as it must be fixed for a good immersion experience) - here is a link for a post if you want to vote those up too:
http://feedback.arma3.com/view.php?id=2256
Also not in these suggestions are blood clouds if hit underwater - here is a link for a post if you want to vote those up too: http://feedback.arma3.com/view.php?id=1718