Oil-sands operators of Fort McMurray, Alberta produce six million t/y of petroleum coke. The use of coke to stabilize clay-dominated mine tailings in constructed wetlands is being studied in landscape reclamation. We studied 'in situ' effects of petroleum coke amendments placed in three wetlands constructed with different materials over two years. Coke amendments did not significantly increase concentrations of trace metals in sediment pore waters or associated biota in plots. Growth of resident macrophyte species was not prohibited by coke amendments. Coke plots in a reference wetland contained fewer stress-intolerant invertebrates, than reference plots, likely due to avoidance of coke substrates. Adding peat reduced 'Chara' cover and biomass in the reference wetland, but had no impact on plants or invertebrates in the wetlands with little organic content. Overall, local coke amendment effects were detected in a reference wetland but not in two wetlands constructed with other oil sands process materials.