Nutrients indirectly affect the quality of fish habitat and indicate the potential for eutrophication—excessive aquatic plant growth—which has been a serious problem. 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. Both total phosphorus and nitrogen are used to indicate potential for eutrophication. Nitrogen is generally the controlling nutrient for salt water systems but can impact freshwater at high concentrations. Nitrate (NO3) scores are based on EPA Ecoregion XIV levels. Nitrate was used as a surrogate for the more comprehensive measure Total Nitrogen which is not consistently measured.