AbstractThe biomagnification of polychlorinated biphenyls (PCBs) and major organochlorine pesticides (OCPs) was studied using lake trout (Salvelinus namaycush) and other food web organisms collected from 17 lakes in Canada and the northeastern United States between 1998 and 2001. Whole lake trout (n = 357) concentrations of the sum (Σ) of 57 PCB congeners ranged between 1.67 and 2,890 ng/g wet weight (median 61.5 ng/g wet wt). Slimy sculpin had the highest mean concentrations of ΣPCB of all forage fish (32–73 ng/g wet wt). Positive relationships between log (lipid wt) concentrations of PCB congener 153, PCB congener 52, p,p'‐dichlorodiphenyldichloroethylene, hexachlorobenzene, cis‐chlordane, trans‐nonachlor, or dieldrin and trophic level (determined using stable nitrogen isotope ratios) were found for most of the 17 food webs, indicating biomagnification of these PCBs and OCPs. The p,p'‐dichlorodiphenyldichloroethylene had the highest trophic magnification factors (TMFs) of the 14 individual compounds studied, averaging 4.0 ± 1.8 across the 17 lakes, followed by trans‐nonachlor (3.6 ± 1.5) and PCB congener 153 (3.4 ± 1.2). Average TMFs for 14 individual PCBs or OCPs were significantly correlated with log octanol–water partition coefficient, implying that the rate of accumulation along the food web is dependent on hydrophobicity and recalcitrance. Significant correlations (p < 0.05) were found between TMFs of ΣPCBs, hexachlorobenzene, α‐hexachlorocyclohexane, and lindane and lake area, latitude, and longitude, but not for 11 other PCBs or OCPs. Overall, the results of the present study show that biomagnification of PCBs and most OCPs, as measured by TMFs, is only weakly influenced by such factors as latitude and longitude. Exceptions are hexachlorocyclohexane isomers and hexachlorobenzene, which had generally greater TMFs in northern lakes, possibly due to lower rates of elimination and biotransformation in the food web.