Dissolved Oxygen (O2)

Dissolved Oxygen is the amount of gaseous oxygen (O2) dissolved in the water. Oxygen enters the water by direct absorption from the atmosphere, by rapid movement, or as a waste product of plant photosynthesis.  Water temperature and the volume of moving water can affect dissolved oxygen levels. Oxygen dissolves easier in cooler water than warmer water.
Adequate dissolved oxygen is important for good water quality and necessary to all forms of life.   Dissolved oxygen levels that drop below 5.0 mg/L cause stress to aquatic life. Lower concentrations cause greater stress .  Oxygen levels that go below 1-2 mg/L for a few hours may result in large fish kills.