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Given the importance of anadromous Northern Dolly Varden as a consumption staple for northern residents and the climate- and development-related impacts on total mercury (THg) concentrations, temporal changes in northern Dolly Varden THg concentrations were assessed between historical (1986-1988) and contemporary (2011-2013) periods from two rivers in the north-western Canadian Arctic. In the Rat River, mean THg changed from 79 +/- 42ng/g ww in 1986-1988 to 109 +/- 44ng/g ww in 2011-2013, while in the Firth River, THg changed from 126 +/- 45ng/g ww in 1986-1988 to 178 +/- 47ng/g ww in 2011-2012. Length adjusted values indicated increases in the Firth River were driven by the increased size of fish, but increases in the Rat River were not. After factoring in size, C-13 and N-15, [THg] was found to be most influenced over time by fish size, but also significantly modified by temporal period and foodweb position. Relationships between log[THg] versus fork-length and log[THg] versus C-13 have remained constant over time in the Rat River, but not in the Firth River, while relationships between log[THg] versus N-15 have remained constant in the Firth River, but not in the Rat River. Changes in the significance and the slope of the relationships relating C-13 and N-15 to log[THg] suggests underlying bioaccumulative processes are temporally variant and will be sensitive to climate-driven changes in the aquatic environments within which fish live and feed.