In this map, I have marked all the places of underwater zones without water, as well as holes in the space of the bottom, through which you can overcome the underwater surface and fall through, followed by the appearance on the nearest road or land tangible by pedestrians.
The blue color indicates the places where the main character swims from floating to walking, the lung volume scale disappears and the player can endlessly walk on the underwater bottom as a pedestrian until he reaches the water surface (on which ships float), until he falls into one of holes or until it runs outside the map where the sandy surface has no collision
In red, I marked the very holes where you can fall while underwater on foot, and some of them you can even swim without using the underwater walking bug