This study aims to determine the toxic effects of heavy metal pollution on carp (Cyprinus carpio) in Sapanca Lake by biochemical and histological analyses. For this reason, fish and water samples were taken from the lake in 2015. Heavy metal (Cu, Fe, Zn, Pb, Cd) analyzes in the water column and tissues (muscle, liver, gill) were determined by ICP-OES. CAT, GSH and MDA levels, which are oxidative stress bioindicators in tissues, were measured by spectrophotometric methods. Histopathological findings in tissues were determined by Hematoxylin-Eosin staining. As a result, heavy metal concentrations in water were determined as Fe > Zn > Pb > Cu > Cd. The accumulation of Cu, Fe and Cd in the tissues of the fish were liver > gill > muscle, and the accumulation of Zn was gill > liver > muscle. CAT activity, MDA and GSH level of the tissues changed with the water temperature. General signs of destruction were observed in the gill tissues of the fish. Necrotic conditions in hepatocytes were observed. In conclusion, the presence of biochemical and histopathological findings in tissues suggests that the lake is not only affected by heavy metals but also by other pollutants.