The master variable in the transport of copper and zinc in lakes is the particle flux. The autochthonous contribution to this particle flux stems primarily from the primary producers. The bioavailability of copper and zinc is strongly influenced by the proton activity in the lake water. Since this property is also a function of primary production a negative feed-back mechanism can be postulated for the biota metal interaction. If the two metals exceed a certain threshold value, the biota adapts itself primarily on the level of the primary producers. This adaption results in a phytoplankton community having a reduced capacity to assimilate trace metals. © 1985 Taylor & Francis Group, LLC.