Any water in a
sea or
lake that is neither close to the bottom nor near the shore can be said to be in the
pelagic zone. The word "pelagic" is derived . The pelagic zone can be thought of in terms of an imaginary cylinder or
water column that goes from the surface of the sea almost to the bottom. Conditions differ deeper in the water column such that as pressure increases with depth, the temperature drops and less light penetrates. Depending on the depth, the water column, rather like the
Earth's atmosphere, may be divided into different layers.