Suspended sediment and extracts of the aqueous phase were collected in 1981 at eleven locations in the Lower Great Lakes Region and analyzed for 17 organochlorine pesticide residues and PCB's. Mirex, and p,p'-DDE when found were predominantly in the suspended sediment fraction, whereas α-BHC, γ-BHC, dieldrin, endrin, p,p'-TDE and trans-chlordane were most abundant in the aqueous phase. Several pesticide residues, notably cis-chlordane, p,p'-DDT and p,p'-methoxychlor were found to have variable distribution characteristics between the suspended sediment and aqueous phases. The greater proportion of organochlorine pesticides present in Lake Erie and the Niagara River were found in the aqueous phase samples, which contained at least 90% of the total pesticide concentration at 5 of the 6 stations sampled. Virtually all of the organochlorine contaminants present in Lake Ontario were found in the aqueous phase, which contained 100% of the pesticides and 91% of total PCB's. Similar results were obtained for the St Lawrence River.

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