Contaminated layer approximately 0,5 m thick and covering 2 800 hectares. Between 1950 and 1990 factories on the banks discharged large quantities of waste materials into the water. The current in lake Ketelmeer is much weaker than in the rivers, as a result of which the mud particles settle on the water bottom. Attached to the deposited particles are waste materials (pollutants) like PAKs, PCBs, and heavy metals. The water and the small sandy beaches along the lake are clean. The contaminated mud is preventing the development of shipping and recreation for the surrounding cities. Sources of pollution have been stopped – ecological function of the lake can be re-established.