This issue of Ambio deals with selected aspects of the many results obtained from the investigations of Sweden´s four largest lakes Vänern, Vättern, Mälaren and Hjälmaren. The issue is dedicated to the professors Thorsten Ahl (1930-1995) and Torbjörn Willén (1926-2000) in memory of their work as creators and leaders of an efficient monitoring and research organization which still is in operation, now with expanded duties i.e. the Department of Environmental Assessment at the Swedish University of Agricultural Sciences in Uppsala. One introductory article, presented here , gives an overview of the large-scaled research projects and their main reflections in the society, and for the design of a present national monitoring system of Swedish lakes. The other articles may be ordered from the authors.