The answer is a "dam."
A wall that holds back water is a dike, levee or dam
levies
A levee holds back water.
it is a dam that holds back water and it blokes the water like lakes,rivers and the ocean.
Earth or concrete/steel dams.
I'll be back
the back seat holds three but seperates into two seats
At a greater depth, there is a greater pressure, period. The amount of water in the dam is irrelevant.
A noun. It is the name given to an obstruction that holds back water.
a dam A barrier constructed to hold back water and raise its level, the resulting reservoir being used in the generation of electricity
Yes, a "dam" is a barrier that holds back water, a real thing.
Hoover Dam