The molecular oxygen in the air is dissolved in water and is called dissolved oxygen.
The dissolved oxygen content in the water is closely related to the partial pressure of oxygen in the air and the temperature of the water.
Under natural conditions, the oxygen content in the air does not change much, so the water temperature is the main factor. The lower the water temperature, the higher the dissolved oxygen content in the water.
The molecular oxygen dissolved in water is called dissolved oxygen and is usually referred to as DO, expressed in milligrams of oxygen per liter of water. The dissolved oxygen in the water is consumed, and the time required to return to the initial state is short, indicating that the water body has a strong self-cleaning ability, or that the water body is not seriously polluted.
Otherwise, it indicates that the water body is seriously polluted, the self-purification ability is weak, and even the self-purification ability is lost.