Dissolved oxygen saturation is calculated by dividing the measured dissolved oxygen by the saturated dissolved oxygen. It is expressed in percentage. Dissolved oxygen in the water mainly comes from the air. The saturation level does not reach the maximum amount which occurs in a natural balanced state. The saturated DO level lowers as the temperature increases. Moreover, atmospheric pressure and salinity also affect the saturation level. For example, 15℃ clean water with salinity of zero at one atmosphere of pressure, has a saturation level of 10mg/L while at 34℃ the saturation level is 7mg/L.