Phosphorus is an essential nutrient for all aquatic plants and algae. Levels above 0.1 mg/L can cause plant growth above natural levels. The state criteria for phosphorus are 0.05 mg/L for the wet season, and 0.03 mg/L for the dry season. Sites 1, 2, and 5 exceeded the state criteria during the wet season, and all sites exceeded during the dry season. However, site 3 showed the highest level of phosphorus ranging from 0.118-1.498 mg/L. The water there usually displayed a greenish-brown color, and frequently had excessive plant growth. Phosphorus is often the limiting factor that determines the level of eutrophication that occurs. Levels exceeding the normal amounts at Kapaa stream may have been caused by industrial wastes, human and animal wastes, along with human disturbance of the land.