The residues of organochlorine pesticides (HCHs and DDTs) in a dated (Cs-137 and Pb-210) sediment core from the Ku double dagger uk double dagger ekmece Lagoon, an urban lake at the southern entrance of the future Canal Istanbul Project, an artificial watercourse, were analyzed with the gas chromatograph equipped with electron capture detector (GC Ni-63-ECD). Concentrations of aHCH and aDDT along the core varied between 0.4 and 469.4 (average 51.4) ng g(-1) dw, and between 0.5 and 72.0 (average 7.4) ng g(-1) dw, respectively. alpha-HCH was the predominant isomer (98%) and followed by gamma-isomer (2%). The highest concentrations of technical HCH were found in the sediments dated 1963-1972, whilst the DDT concentrations had their maximum around 1945. The highest concentrations of gamma-HCH and p,p'-DDT exceeded probable-effect level values which can lead to frequently cause adverse effects on aquatic biota.