When considering the issue of the functioning of small water reservoirs, the attempt to assess changes in trophy of small retention reservoir located in Wasilkow, Podlasie, before and after remediation, was carried out. Water samples tests were carried out once a month from April 2007 to March 2008, from April 2009 to March 2010 (before remediation), and from April 2013 to March 2014 (after removal of silt). Prior to works related to the reservoir remediation, a gradual increase in the number of tested contaminants and disturbances in the seasonal occurrence of nitrogen and phosphorus compounds were observed. Advanced eutrophic processes in Wasilków reservoir occur probably due to the supply of large amounts of humic and biogenic substances from the catchment, because a significant percentage of its area is covered by forests and agricultural lands. The development of the trophic status of the reservoir is largely influenced by the amount of phosphorus and total nitrogen supplied to the reservoir; the least affected by chlorophyll “a”. Comparing the analyses performed in 2007/2008 and 2009/2010, a slight, but growing trend of average trophic levels of water in the basin Wasilków was found. Studies conducted in 2013/2014 revealed a significant decrease in the concentrations of all analyzed pollutants, and hence lower TSI values. It can be concluded that the reclamation associated with the removal of sediments brought the expected results.