The Convention on the Protection and use of Transboundary Watercourses and International Lakes requires that water quality objectives and criteria shall: (a) Take into account the aim of maintaining and, where necessary, improving the existing water quality; (b) Aim at the reduction of average pollution loads (in particular hazardous substances) to a certain degree within a certain period of time; (c) Take into account specific water-quality requirements (raw water for drinking-water purposes, irrigation, etc.); (d) Take into account specific requirements regarding sensitive and specially protected waters and their environment, e.g. lakes and groundwater resources; (e) Be based on the application of ecological classification methods and chemical indices for the medium- and long-term review of water-quality maintenance and improvement; and (f) Take into account the degree to which objectives are reached and the additional protective measures, based on emission limits, which may be required in individual cases.