[QUOTE=Xema]
Water is nearly incompressible, so there’s no meaningful increase in density. But there is an increase in pressure with depth, which can be explained as the deeper water supporting the weight of the water above it.
[/QUOTE]
Right. When you’re designing a dam, for example, the depth is used, while how long/big the river/lake is is not. The free body diagram will show the force on the dam as a triangle, with zero pressure on the top and rho g h (densityforce of gravitydepth (height) of the fluid).