I think the background information needed to answer this question is missing. Where was the sand surface that the water was below, and why is it important to know what happens to it?
With those clues a answer would be possible.
Water table
Well water
beneath the surface
no Not on the surface; some speculate that there may be frozen water beneath the surface.
Only from the sides and from beneath
Magma that has come to the surface is then referred to as Lava.
An ocean current?
buoyancy
Yes.
itr means a dam
Groundwater is water that is stored in layers of soil and rock beneath Earth's surface. It fills the spaces between particles of rock and soil and can be accessed by wells or springs.
Various mysterious creatures, such as lake monsters or unknown aquatic species, could potentially be hiding beneath the surface of the dark lake water.