Changes in depth and decrease of the sediment rate before and after a building breakhead maintenance construction were studied in small monomictic and eutrophic Lake Fukami-ike in central Japan. The maintenance of farm village drainage and the waterfront function was carried out for the activation of the town in 1992, and the water quality improvement was expected. However, variations of transparency were observed and no blue-green algal bloom outbreak had occurred before recently observed. Maximum depth changed from 9.3 m (1951), 8.5 m (1979), 8.1 cm (1992) to 7.8 m (2012), respectively. Changes in the autochthonous and allochthonous matters in the lake were thus considered. Sediment rates of 19.5 ± 10.19 gm -2 d - 1 (1978 to 1979) and 4.40 ± 2.27 gm -2 d -1 (2007 to 2008) were observed, and decreased 22.6%. These deposition rate data corresponded to 3.1 cm year -1 (1979) and 1.2 cmyear -1 (2009), respectively. The decreased percentage of organic matter and the reduced deposition rate were because rice fields and forest around the lake give way to take concrete roads. It was considered to be because the inflow of sediment stopped when it rained, and allochthonous inorganic matter was significantly reduced.