Murky water
Directors occasionally have to make choices based only on appearance, and they have to give up some credibility in the process. We never realized that even the water doesn’t appear exactly as it should have when we viewed Titanic.
The water would actually be muddy, considerably darker, and teeming with marine life. That would have been far more true to life, but it would have been extremely difficult to film and would have presented a challenge for cinematographers as well.
