Normally, one can tell when he's about to hit the water BEFORE he actually hits it. Most people aren't watching the altimeter in a fight, if fact, when zoomed into the sight, most people can't even see the altimeter on their screen
...one greatly underestimates the power of "misjudgment of altitude due to lack of visual markers above flat terrains."
It's probably one of the most frequent of reasons behind airplane crashes, other than mechanical failures... and there is good reason why flight schools teach instrumental flight - learning to trust what your instrument reads and fly accordingly, rather than trusting what you actually see, since in many cases, your eyes fool you.
Besides, it can only mean that flying over water at low altitudes, and getting into a maneuvering contest is a dangerous thing which people should try to avoid... which, I don't see anything wrong with.
So, like I've said before, we have pretty water, and we also have people being alarmed about fighting over large bodies of water at lower altitudes.. two realism points at the price of one..
I call this a Win-Win.