Rivers Data show water quality of selected rivers. Water quality is measured in terms of annual mean concentrations of dissolved oxygen and BOD; of nitrates, phosphorus and ammonium; and of lead, cadmuim, chromium and copper. The rivers selected are main rivers draining large watersheds in the countries chosen; the measurement locations are at the mouths or downstream frontiers of the rivers. These parameters provide information concerning the state and trends of pollution by organic matter and nutrients, heavy metals and other metals. In reading the data, one should compare trends rather than absolute values, since measurement methods vary by country. Lakes Data show trends in annual mean concentrations of phosphorus and nitrogen in selected lakes. These parameters concern nutrient concentrations and related degrees of eutrophication of lakes and reservoirs. The interpretation of these tables should take into account variations in the methods of sampling (e.g. sampling location and number of measurements at different sampling locations and in different years).