When the dissolved oxygen levels drop too low, the fish will either die directly from asphyxiation or days later due to disease outbreaks caused by stress associated with low dissolved oxygen. Farm ponds normally have a faint green color, and the water should be clear enough to see around 2.5-3 feet vertically into the pond water. Water clarity decreases as a result of these alga blooms to the point that your hand is not visible in as little as six inches of water. If these alga blooms are followed by periods of cloudy weather, there will be a potential of an alga die-off. The cooler the water the more soluble the gas.
Water has a high-heat capacity and unique density qualities.
In spring, water temperatures are nearly equal at all pond depths. As a result, nutrients, dissolved gases, and fish wastes are evenly mixed throughout the pond. As the air temperature increases in the summer, the surface water becomes warmer and lighter while the cooler-denser water forms a layer underneath. Circulation of the colder bottom water is prevented because of the different densities between the two stratified layers of water. Dissolved oxygen levels decrease in the bottom layer since photosynthesis and contact with the air is reduced.