Up to the 1980ies, wastewater inputs from industry and households were the most important source polluting rivers with nutrients and noxious substances. The development of wastewater treatment plants considerably reduced pollution from these point sources. Diffuse pollution of water bodies through the air or the soil continue to be problematic.
Nitrate washed out from agricultural surfaces and reaching rivers and lakes through the soil and ground water is a classical example of diffuse pollution. Analysis has shown that the nutrient and pollutant content in the Rhine basin is still too high. Problematic pollutants are heavy metals such as chromium, copper, zinc and nickel as well as PCB and hexachlorobenzene which are largely remnants of former inputs or of diffuse origin.