A methodology has been developed to help protect lake water quality from degradation by nutrients. Criteria have been established which are keyed to protect the most sensitive water use of the lake. The categories of water use include aquatic life (including fisheries), recreation and aesthetics, drinking water, agricultural use, and industrial use. These criteria are the basis for more specific water quality objectives that are tailored to individual sites—either lakes or portions of lakes. Phosphorus concentration was chosen as the primary means of quantifying water quality, although nitrogen also can be used where it is the limiting nutrient. For phosphorus-limited lakes, the criteria used to protect drinking water and recreation are 10 μg/L total phosphorus. Criteria for fisheries and aquatic life differ according to important species. For example, for lakes with important salmonid fish resources, the criterion is a phosphorus concentration between 5 and 15 μg/L. For stratified lakes with important warmwater fisheries, a phosphorus concentration of 10–40 μg/L has been proposed. These criteria have been proposed specifically for British Columbia and may not be directly applicable to other areas.