The area at the very bottom of a waterfall where the water strikes the ground or a riverbed is most technically known as a plunge pool. This is a deep, often circular basin that is carved out over centuries by the sheer hydraulic force of the falling water and the abrasive action of rocks and sediment swirling in the current. In some geological contexts, it may also be referred to as a "catchment basin" or simply the "base" of the falls. Plunge pools are fascinating ecosystems because they are highly oxygenated due to the constant churning of the water, though they can be extremely dangerous for swimmers due to powerful "recirculation" currents and hidden debris. If the waterfall does not fall into a deep pool but instead hits a series of broken rocks, that area is called a talus slope or a "rock pile." For photographers and nature lovers, the plunge pool is often the most dramatic part of a waterfall, where the energy of the vertical drop is finally transformed into a mist-filled, roaring display of natural power.