Abstract.-Many indices have been developed to evaluate the environmental risks of heavy metals in sediments. In the present study, two of these indices were used to determine the sediment quality of a polluted freshwater ecosystem. Sediment samples were collected seasonally from seven stations selected on Felent Stream and the accumulations of some heavy metals (As, Cr, Cu, Pb, Zn) in sediment were investigated seasonally. Potential ecological risk analysis (R I ) and biological toxicity test based sediment quality guidelines (mERM-Q) applied to the results to assess the environmental risks of heavy metals in the region (As, Cr, Cu, Pb, Zn). According to the results, Köprüören and Yoncalı Villages (F2 and F3 stations) where mining -agricultural sections of the study area were "high -medium priority site" according to mERM-Q and has "moderate ecological risk" according to R I . Kütahya Province and estuary of stream (F6 and F7 stations) where urban sections of the study area had "high -medium priority site" and "medium -low priority site" respectively according to mERM-Q
