Lake Kasumigaura, the second largest lake in Japan, is an extremely eutrophicated lake, yet is one of the most important water resources around the Tokyo metropolitan area. It is a shallow lake with an average depth of 4 m. Nutrient exchange between the lake water and sediments was found to be the major factor affecting the nutrient balance within the lake. Therefore, it was decided to carry out dredging of sediments along with other measures to control eutrophication of the lake. To dredge fluffy sediments on the top layer effectively and to avoid excessive disturbance of the sediments, a special purpose dredge equipped with the Oozer system was built, and later, a modified version was constructed. The engineering aspects of dredge efficiency are summarized in the paper based on the 5-year experience.