Shallow water reservoirs (usually up to 2 meters deep), with no outlet, replenished mainly by precipitation and shallow groundwater. Ponds can be created naturally (natural depressions filled with water) or made artificially (pools made from concrete or prefabricated components, and earthen ponds dug in a place suitable for breeding), and they can be drainable or undrainable. Usually, natural ponds are not drainable, while artificial ponds may belong to both types.