Created wetlands of the Fort McMurray post‐mined landscape have been amended with oil sands processed substrates (CT, MFT) and water (OSPW). Plant species found in these wetlands appear to tolerate the salinity and toxicity (Naphthenic Acids, Heavy Metals) of the processed materials. They offer an opportunity to identify plant mechanisms responsible for their ability to tolerate polluted wetlands. We propose that plants growing in wetlands amended with oil sands processed material may demonstrate measurable biological stress symptoms even though their physical appearance and performance seems to remain unaffected. We studied Carex aquatilis, an abundant wetland plant species in the Fort McMurray region in five natural (reference), and ten affected wetlands. We measured plant physiological processes: photosynthesis, transpiration rates, stomatal conductance, and leaf fluorescence. Our results show that C. aquatilis critical physiological processes, including carbon assimilation and water economy, are not significantly different between treatments. On the other hand, processes related to leaf light use efficiency (Fv/Fm, Performance Index) were significantly higher in plants growing in oil‐sands‐affected wetlands. Results suggest that processed materials can positively affect some plant photosynthetic stages but they are fully compensated and have a non‐significant impact in the entire carbon assimilation process. Our results are coherent with previous research that suggests that processed materials slightly and positively enhance Typha latifolia performance.