Question

Why does fluid pressure increases with depth?

Answer 1

Pressure is defined as force per unit area. As you move further down a column of water, there is more water to provide a downward weight on an object, therefore the FORCE increases, as a cross sectional area stays constant, and thus PRESSURE increases

Answer 2

Because for any level bit of area you look at, the deeper that bit of surface is, the more weight of fluid there is above it. Water pressure ... or air pressure for that matter ... is just the weight of water or air on that surface, from there all the way up to top of the lake, or the atmosphere.