The trace elements Pb, Cd, Cu and Zn were assayed in settling particles (tripton), biota (zooplankton, Asellus aquaticus, midge larvae, the moss Drepanocladius fluitans and the reed Phragmites australis) and profundal and littoral sediments from a dam reservoir of the Vistula River and a nearby forest lake and from six further lakes within the Masurian lake district and the Brodnica Park area. The amounts of metals in tripton differed greatly between lakes, while concentrations in zooplankton were almost homogeneous; only for an acidified clearwater lake (pH 4.8) were exceptional Pb and Cd levels recorded in zooplankton (56 mg Pb kg-' and 12.8 mg Cd kg-' d.w.). Similarly elevated levels were found in A. aquaticus, suggesting a metal-mediated retardation in growth of isopods in this lake. Great variability was also noted for profundal sediments, with highest concentrations in the Vistula dam reservoir, reaching 9-12 mg Cd kg-' and 580-730 mg Zn kg-' d.w. Apart from these exceptional values, most of our data were well within the reported literature range. Nevertheless, only Cu concentrations in profundal sediments of the lakes investigated are (with two exceptions) smaller than threshold effect levels below which biological effects are unlikely to occur.i In memoriam R. ZYTKOWICZ who died on 9 June 1994.