A paleolimnological assessment of Lac de Gras (Northwest Territories, Canada) showed pronounced aquatic ecological and biogeochemical changes occurring since at least ~1950, well before diamond mining operations began in 2000. Three sediment cores were collected from the eastern end of Lac de Gras, near to the Diavik Diamond Mine, dated using 210Pb radioisotopes, and analyzed for metals, organic carbon, nitrogen stable isotopes, and diatoms.