Oxygen gas dissolved in water is essential for the existence of most aquatic organisms. It is needed for their cellular respiration. Dissolved oxygen (DO) concentrations range from 0-15 mg/L. A high DO level indicates a healthy stream where diversity of organisms exist. As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life is put under stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills.

In Kapaa stream, all the sites measured DO levels ranging from 1.15-8.34 mg/L. The measurements on 11/22/03 were particularly low. From our observations on that day, there were an abundance of aquatic plants on the surface. DO can decline dramatically following decomposition of aquatic plants.