Since the establishment of ICP Waters in July 1985 under the Convention on Long-range Transboundary Air Pollution, the programme has documented effects of reduced emissions of acidifying components on surface water quality and biological status of lakes and rivers in acid-sensitive areas. Additionally, ICP Waters has documented concentrations levels of heavy metals and POPs in sediments, waters and fish in remote areas untouched by local sources of pollution. ICP Waters has contributed to substantiate relations between critical load calculations and empirical data. Unexpected effects of reduced acid deposition have been documented such as the widespread increase in DOC leading to browning of surface waters. The programme has maintained high quality of the reported data offering a manual with recommended methods, an annual intercalibration of chemical analyses and biological classification of invertebrates. The ICP Waters database now contains over 10 to 20 years of data from ca 200 sites in 18 countries Europe and North America. International cooperative work on emission reductions to abate surface water acidification has so far been very successful, but there is still a long way to go. Among the major uncertainties in the future chemical and biological recovery are the effects of climate change and the future behaviour of nitrogen in the ecosystem.   Continuation of national monitoring programmes that submit their data to ICP Waters and the yearly chemical and biological intercalibration exercises are the most important key activities for documentations of recovery from acidification.