Ketelmeer, a lake in the Netherlands with a length of some 10 kilometers and a width varying from two to three kilometers, separates the North Eastern and Southern Polders constructed during the late 1960s and early 1970s. It is a major example of the problem of 'historic pollution'. Lake Ketelmeer receives the waters of the Rijn and IJssel and over a period of three or more decades, tens of millions of cubic meters of highly contaminated sediments entered Ketelmeer from hundreds of upstream locations. The bottom was covered by polluted sediments to an average depth of 50 cm. A significant proportion of this material had to be removed, or capped by the cleaner sediments of recent years, if a normal aquatic environment was to be restored.