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Due to a fast decline in the ecological quality of watercourses combined with the threat of human functions, policy makers started to legislate water quality objectives for watercourses and to set up water purification programs. The description of universal quality objectives is too limited as a frame of reference and a policy only based on water quality cannot guarantee the goals of river restoration as a whole. In most countries the need for a more integrated approach of water management is growing. Water quantity must be managed together with water quality, surface water with groundwater, and the water economy with town and country planning.To restore and maintain the natural diversity of watercourses, together with the natural species richness, policy makers need a frame of reference based on the natural functioning of the ecosystem. The highest level of reference is called the 'ecological naturalness'. Based on the present and the potential ecological value and on the intensity of human uses, policy makers together with a group of scientists should decide on the ecological quality objectives of watercourses. The lowest quality level that must be reached in all watercourses can be described as the 'ecological basic quality'. Together with a frame of reference, there is a need for a refined ecological evaluation method for ecological quality as a whole, and especially to evaluate 'potential ecological values' in an objective way.