Mercury flux and fate (whether mercury was retained in the aquatic ecosystem or exported to the riparian ecosystem via blackfly emergence) was calculated based on animal consumption rates and total mercury concentration of diet items. Consumers and their gut contents were collected at six sites on the Colorado River in the Grand Canyon. Sites ranged from 0-367 river kilometers downstream of Lees Ferry (AZ, USA). Organic matter types and animal tissues were analyzed for total Hg using cold vapor atomic fluorescence (CVAF, Tekran Model 2600 CVAF spectrometer) following EPA Method 7474. Gut content samples used to calculate consumption rates were collected at least quarterly from July 1, 2007 to June 30, 2009. Organic matter types and consumers were collected June 12-28 2008. Data provided in this report include animal consumption rates; total mercury concentrations of food web samples and mean mercury concentrations of diet items; total mercury fluxes from diet items to individual consumers; the total amount of mercury in blackfly larvae that was consumed by fishes, excreted during metamorphosis, or exported via adult blackfly emergence; site locations and river widths; and the total flux of mercury at the scale of entire invertebrate and fish assemblages.