On the intro you see the Minnow sitting on the beach, but the water isn't ocean water because there are no waves crashing into the shore, the water is just sitting there like fresh water does.
I know that it wasn't really the ocean, but on calm days in certain areas, the ocean doesn't "crash" up against the shore anyway. I go to the beach all the time, and there are times when everything is very peaceful.
This is because if you look it is a smaller part coming from the ocean almost like a bay. I live by a bay and go there all the time, there are no waves at all.