There's no sea in HZD...
Patched water :
To save ressources. It's obvious and i think they made the right choice since the water looks good enough to me. If you want to see real ugly water, play to God of War lol...
It usually means a lot more complex scripts and gameplay mechanics. Also, your engine has sometimes to deal with fancy cutscenes. And it's not a easy task. For instance, ROTR is native 4K on X, but not the cutscenes...
Water itself still isn't accurate and the reflections aren't improved at all. That's my biggest gripe with hzd water.
Also here's the sea you can view in hzd