I have had ACL surgery on both my knees. The last one was almost 8 years ago. I have been riding with knee braces ever since. I only use them for wakeboarding. I don't wear them for any of the other sports I participate in.
In my experience, non of the existing braces work very well in a wet environment. I'm not knocking the manufacturers, it's just that, as far as I know, no one has designed a brace specifically for use submerged in water.
Here is what I have done to my braces to make them almost perfect for use in water:
With this setup, once they are on I don't even think about them. They don't move, or get loose, they just work!
Good luck with your search,