As a pond is basically a stagnant body of water, it needs to be kept fresh through some kind of aeration system in order for algae to not be able to take over the pond, making it unsightly and smelly. In order to remain fresh, water needs to have contact with the air from which it can draw oxygen as it is a lack of oxygen in the water that will kill any fish life and promote the growth of algae. Any system which allows a body of water to come in regular contact with the air it requires is known as an aeration system and there are several kits available that allow for easy pond aeration. When selecting a kit to use on your pond, you will first have to establish the depth of the pond as there is aeration systems designed for ponds with a depth of no more than 6 feet and others for depths deeper than that. Perhaps one of the most popular aeration systems for a shallow pond is a fountain which, apart from providing a pond with effective aeration, can also improve the look of a pond, giving it character. In recent years floating fountains have started to become popular as they are more versatile, allowing a pond owner to be more expressive in how they want their pond to look. A fountain is an efficient aeration system as it allows the water that it tosses into the air, to come in contact with that air and thereby receive the oxygen it needs. As the fountain also creates a water circulation, it ensures that all the water in the pond is tossed up on a regular basis. The circulation that the fountain creates though, will only cover the first 6 feet of water and so fountains are not effective in deeper ponds. Another popular aeration system that also creates a circulation in the water of a pond is a propeller system. The propeller system consists of propellers spinning at the surface causing the water to become agitated and in that agitation the water comes into contact with the air and becomes oxygenated. For ponds with a depth of more than 6 feet also need the water at the bottom to be aerated, a diffusion aeration system is recommended. A diffusion system consists of 3 main parts, a compressor, an air hose and a diffusion unit. The diffusion unit is placed at the bottom of the pond but is connected to the compressor at the side of the pond, by the air hose. As power is provided to the compressor it sends air through the hose to the diffusion unit which then releases that air into the water. As air will automatically head for the surface and the diffusion unit is at the bottom of the pond, all the water in the pond has the opportunity to react with that air and thereby receive oxygen, aerating the whole pond regardless of depth.