The accumulation of heavy metals (Cu, Ni, Zn, Cd, Pb, Cr, B, As) was measured in water, plankton and sediment samples taken from different areas of Lake Uluabat during January 2003 to February 2004. The sequential extraction used in this study is useful to assess the potential mobility of heavy metals in the sediment indirectly. In this study, Cu, Pb, Cr, Cd, Ni and Zn concentrations were detected at higher levels at Lake Uluabat for selected stations, especially in plankton samples. The magnitude of heavy metal concentrations in water and plankton samples was determined as B>Zn>As>Cd>Pb>Ni>Cr and Zn>Ni>Cu>Cr>Cd>Pb, respectively. The mobile heavy metals in sediment samples were sequenced as Pb>Cu>Cr>Ni>Cd>Zn, whereas the magnitude of easily mobilizable metal concentration was determined as Pb>Ni>Cr>Cu>Cd>Zn. Concentration of Cu and Cr in mobile fraction is detected higher than in easily mobilizable fraction. Concentration of Pb, Cd, Zn and Ni in mobile fraction is detected in lower levels than in easily mobilizable fraction.