3ds max 2016
When creating a surface submerged in sea water,
Theoretically, it’s the Volume Absorption or ‘Fog‘ of the water shader that should do cause the surface to disappear under water.
But in many cases that doesn’t work well because we don’t actually model enough extended surface under the water for it to completely disappear without seeing the surfaces geometric edges that spoil the result.
One of the oldest tricks in the book is to use a Gradient Ramp map in the surface’s Opacity channel to make it gradually disappear before the geometry ends.
This can be done in most 3d software and render engines, I’m demonstrating it here using 3ds max and V-Ray: