The aim of the study was to assess the ecological risk of five trace metals, i.e. Cd, Cu, Ni, Pb, Zn, accumulated in bottom sediments of young water reservoir – Bardowskiego Lagoon located in Warsaw, Poland. In this case, several indices were used, i.e. Geoaccumulation index (Igeo), Contamination factor (CF), Potential ecological risk factor (ER), Degree of contamination (DC), Pollution load index (PLI) and Risk index (RI). The average trace metals concentrations in sediments, were as follow: Zn > Pb > Cu > Cd > Ni. The obtained results revealed that bottom sediments were very highly to extremely high contaminated by Cd and the ecological risk related with this pollutant was the largest. They also indicated that water from the study area was characterized by a low ecological quality, especially due to the content of Cd and Pb. The research proves that problem of cadmium contamination in bottom sediments of young water reservoirs is real and poses a serious ecological risk.