Oxygen is critical for the health of your lake and its fish. Oxygen is dissolved in water from two sources, either from the air or from aquatic plant photosynthesis. Oxygen dissolves into the pond later from the air as the two are mixed together through wind and wave action. Mechanical aeration using pumps, sprayers, and paddlewheels can also be used to increase dissolved oxygen levels during periods of low oxygen. This is often used in small ponds that lack the necessary fetch (length of open water) to have adequate wave action for oxygen mixing. Once again, we can see that lake construction is an important part of lake management, even before the lake exist.
Photosynthesis is the other source of dissolved oxygen. In this process, plants produce oxygen while taking food from carbon dioxide and water in the presence of sunlight. Algae release this oxygen directly into the water during photosynthesis. Since photosynthesis is driven by the energy of sunlight oxygen production occurs during daylight. Therefore, dissolved oxygen concentrations in ponds tend to rise throughout the day. At night dissolved oxygen slowly declines as fish, insects, zooplankton, bacteria and algae consume oxygen through respiration.
Under normal conditions dissolved oxygen concentrations should not fall below 3 or 4 parts per million (ppm). Oxygen concentrations below 3 ppm stress fish and many fish will suffocate at concentrations below 2 ppm. Learning to identify potential oxygen issues is part art, part science, and a good skill for any lake manager to posses.