Concentrations of zinc and copper in a series of large oligotrophic lakes on Vancouver Island, Canada, have been increasing since mining operations began near the south end of Buttle lake in 1966. Declines in species diversity of both phytoplankton and periphyton have occurred since the beginning of mining activity with the disappearance of metal sensitive forms such asAsterionella andRhizosolenia. Cladoceran and calanoid copepod numbers and species diversity increase as the metal concentrations decline downstream from the mine. Bioassays carried out withDaphnia pulex show increasing toxicity downstream. Metal concentrations in Zooplankton and metallothionein concentrations in rainbow trout liver are correlated to metal concentrations in the water. The water was not acutely toxic to rainbow trout in laboratory simulations of Buttle Lake conditions or duringin situ exposures (1 month). Specific sublethal deleterious effects have not yet been determined.