Aeration systems are needed for ponds and lakes because they have the ability to keep a pond or lake fresh. In order for a pond to remain healthy, capable of sustaining fish life, the water in that pond must receive an adequate amount of oxygen on a regular basis and that is what the aeration system does, enables the water to receive oxygen. Water will draw oxygen from the air when it makes contact with it but as a pond will normally only allow the surface water to come in contact with the air, the lower water becomes unhealthy and promotes the growth of algae. As time goes on the amount of unhealthy water exceeds the amount of healthy water near the surface and the algae take over the whole pond creating a smelly eyesore. An aeration system stops this from happening and there are several types of aeration system, divided into two categories, those for shallow ponds with 6 feet of depth and those with more depth. With a shallow pond a popular pond aerators solution is to use a fountain. The popularity of this system is perhaps obvious as; as well as providing an efficient aeration system, a fountain can also add character to any pond and that is becoming even more increasingly so as floating fountains have now become available to purchase. Not only does a fountain throw water in the air which allows that water to come in contact with the air and therefore absorb the oxygen it needs but, the fountain also creates a circulation in the pond’s water, ensuring that all the water in the pond is thrown up on a regular basis. Another popular solution for a shallower pond is a propeller system. A propeller aeration system is different from a fountain as instead of throwing water up in order to allow it to be aerated; the propellers agitate the water allowing it to be aerated that way. Like a fountain though, the propeller system also creates a circulation in the pond’s water, allowing all the water to be adequately aerated. As the circulations created by both the fountain and the propellers will not affect water which is deeper than 6 feet, for the deeper ponds a diffusion system is needed. A diffusion aeration system consists of a compressor, a diffusion unit and an air hose that will allow air to pass between the two. As the compressor is located at the side of the pond and is connected to a power source, it can push air through the hose to the diffusion unit which is located at the bottom of the pond. As diffusion unit releases that air into the bottom of the pond, the air aerates the water on its way to the surface, ensuring that all the water in the pond, regardless of its depth, is properly aerated. As ponds can be located far from a mains source of power, some aeration systems now come complete with their own power source.