In order to study the heavy metal levels of Izmit bay four stations were selected. The study was carried out seasonally between December 2015 and September 2016. This research was conducted to determine heavy metal levels (Al, Cd, Cr, Cu, Fe, Ni, Mn, Pb, and Zn) in seawater, Ulva lactuca L. and Enteromorpha sp. were identified by using ICP-OES. According to the results of this study, heavy metal levels were arranged in the following sequence: Fe > Al > Zn > Cr > Mn > Cu > Pb > Ni > Cd for Ulva lactuca, Fe > Al > Mn > Zn > Cu > Cr > Pb > Ni > Cd for Enteromorpha sp. It was determined that Fe was the highest metal in the Ulva lactuca, Enteromorpha sp.. Heavy metal concentrations at the samling stations may be used for background levels for interspecific comparison with the Izmit Bay. Besides, physical and chemical parameters of sea water were determined. Water temperature, pH and conductivity varied from 10.11-24.22 degrees C, 7.45-8.25, dissolved oxygen values as 8.10-12.70 mg L-1, respectively.