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Oxygen, Temperature and Altitude

The first thing you need to know about oxygen and water is that there are two main factors that set the limits on how much oxygen can be “held” by a freshwater lake: temperature and altitude.

all aquatic organisms use dissolved oxygen gas (O2 ) that is constantly entering water from two main sources: the atmosphere and from photosynthesis. 3

Oxygen from the atmosphere continuously enters the surface of a waterbody through a process known as diffusion. Molecule by molecule, oxygen gas (02 ) is pushed into the water by pressure from the air above. Wind and wave action can accelerate the diffusion process because waves create more surface area for oxygen to enter the water.

What is the “normal” dissolved oxygen concentration in freshwater systems? In most freshwater environments, DO measurements usually range somewhere between six and ten milligrams per liter (mg/L). When measurements drop down to three or four milligrams per liter, fish and other aquatic life will begin to experience stress, especially if the drop in oxygen occurs suddenly. Few organisms are able to survive in water when dissolved oxygen levels are below 2 milligrams per liter.

In most freshwater environments, DO measurements typically range between six and ten milligrams per liter (mg/L). At three or four milligrams per liter, fish and other aquatic life will begin to experience stress.