Nutrients indirectly affect the quality of fish habitat and indicate the potential for eutrophication—excessive aquatic plant growth—which has been a serious problem in the watershed. The overgrowth of algae and aquatic plants leads to large daily changes in dissolved oxygen and pH levels which affect fish habitat. Eutrophication can also severely impair enjoyment of the river’s scenery and use for recreation. Phosphorus is generally the controlling nutrient for freshwater systems. Both phosphorus and nitrogen concentrations are used to indicate potential for eutrophication. Total phosphorus (TP) scores are based on EPA Ecoregion XIV levels.