A cascade of water falling from a height, formed when a river or stream flows over a precipice or steep incline. Waterfalls are known to be relaxing and peaceful. Scientifically, there are claims that negative ions that are abundant in waterfalls somehow increase serotonin levels, which ultimately helps our mood. The mental health aspect comes from the relaxation-tendencies we'd tend to have from the simple act of watching the motion and sound of moving water. The movement of water at the top of a waterfall can flatten rocks at the edge. The plunge pool at the base gets bigger as rushing water and sediment erodes it and the area behind the waterfall is worn away, creating cave-like shelters. As they flow into the different rivers, waterfalls purify the water. Purification of water helps the different aqua life to live through provision of oxygen. Waterfalls also help in turning waste that runs in the water into nutrients which help plants to grow.