This study assessed the geographic distribution of mercury in water, and biota of the Athabasca River, and in snow and vegetation in its watershed. Mercury in the snowpack was significantly elevated within 46km of oil sands development relative to greater distances. Mercury was significantly higher in tributaries more disturbed by oil sands development relative to less disturbed watersheds. Mercury in vegetation was elevated near development, but was higher at moderate distances from development, likely due to differences in atmospheric speciation within upgrader plumes compared to speciation within the downwind atmosphere. Mercury concentrations were significantly higher in Walleye, Northern Pike, and Goldeye compared to Lake Whitefish. A large percentage (72-80%) of Northern Pike, Goldeye, and Walleye exceeded the Health Canada fish consumption guideline for frequent consumers. The spatial distribution of mercury within the Athabasca River and its watershed indicates oil sands development is a significant source of mercury within the region.