Estimates of wildlife population viability through measurements of contaminant stressors, such as water mercury concentrations, were modified with variables specific to New York’s Adirondack Park to develop a wildlife criterion value for the Common Loon (Gavia immer). Biotic and abiotic samples were collected for mercury analysis on 44 Adirondack lakes over a 2-year period (2003 to 2004). From 1998 to 2007, Common Loon blood samples were collected for mercury analysis from the 44 lakes, loon feather samples from 40 lakes, and nonviable eggs from 29 lakes. It was determined that 2.00 ng Hg/L or less in the water was small enough to prevent male Adirondack Common Loons from accumulating mercury in levels high enough to impact reproductive success and behavior, while a water sample of 1.69 ng Hg/L or less was small enough to not cause impacts to female Common Loons. These wildlife criterion values are greater than the wildlife criterion value of 1.30 ng Hg/L applied to avian species by the Great Lakes Water Quality Initiative. The Common Loon-based wildlife criterion value provides a valuable estimate of the mercury thresholds associated with biotic impacts due to mercury contamination in aquatic ecosystems, enabling legislators to integrate these standards into policies that better protect environmental quality. Based on the water samples collected, it was estimated that the wildlife criterion value accurately predicted the protection of 61% of female and 73% of male Adirondack loons. More rigorous sampling of the abiotic compartment over a wider temporal and spatial scale is necessary to fully understand how water quality parameters relate to Common Loon reproductive success.