Dissolved Oxygen Levels in Water: Riverwood Fish Kill?

Dissolved oxygen is essential for living organisms in water, however, too much or too little can be fatal. Since the solubility of gas within water decreases as temperature increases, the high temperatures of the hot summer months can create problems for dissolved oxygen levels in water. Fish are cold blooded creatures, meaning the temperature of their blood adjusts to the temperature of the surrounding environment. High temperatures cause the metabolisms of fish to increase. This makes the fish need more food, more exercise, and therefore, more oxygen. When the fish consume more oxygen, there is less oxygen in the water, and although it may sound ironic, fish suffocate when there are low dissolved oxygen levels in their waters.
There is also such thing as too much dissolved oxygen levels in water. Since oxygen and nitrogen are atmospheric gases, when there is dissolved oxygen in water, there is also dissolved nitrogen. During times of low temperatures in water or distribution of large quantities of air into water (see dam picture), water can become a supersaturated solution, with 110%-124% oxygen gas and nitrogen gas saturation. Although oxygen may be partially utilized by fish during metabolism, nitrogen gas clogs the capillaries of the fish, which leads to the development of bubble trauma syndrome. Not only does this kill fish, but it can only be diagnosed promptly after death through careful dissection of gills in search of gas bubbles.

Too little dissolved oxygen in water:

Too much dissolved oxygen gas *AND nitrogen gas in water: this creates supersaturated water with oxygen and nitrogen gas.