Aeration systems circulate air through water in order replenish the water's oxygen levels. The more air that is pumped into the water the better the circulation, thus reducing chances of bacteria build up and stratification. This process is most commonly used with stagnant bodies of water such as lakes, ponds, farm dugouts, reservoirs etc. The oxygen that is pumped into the water is extremely effective in breaking down organic matter and sludge (beneficial bacteria that culminates at the bottom).