The atmospheric deposition of mercury on New Hampshire's landscape impacts wildlife. The information presented in this report describes impacts on the Common Loon and its unusually high risk to mercury (Hg) in southern New Hampshire. Past models generated by the U.S. Environmental Protection Agency predict particularly high levels of Hg deposition in the southern part of New Hampshire. Beginning in 1994, a collaborative effort by members of the Northeast Loon Study Working Group, including BioDiversity Research Institute, the Loon Preservation Committee, and the U.S. Fish and Wildlife Service responded to the model-generated outputs by non-lethally collecting eggs from abandoned nests and blood samples from live loons. Between 1994 and 2000, 375 egg and adult blood samples were collected in New Hampshire, including 266 samples south of the White Mountains. These samples represent 65 loon territories and 47 southern New Hampshire lakes. Laboratory analysis shows that statewide mean Hg levels in New Hampshire eggs and blood are some of the highest in the nation. Although mean egg and blood Hg levels between northern and southern New Hampshire were not significantly different, those levels from nine loon territories on six lakes in southeastern New Hampshire were significantly higher than other regions of the state. A risk assessment for New Hampshire's breeding loons indicates at least 19% of the population (i.e., individuals higher than the lowest observed adverse effect level) is at risk to physiological, behavioral, or reproductive impact. Loon individuals at risk to high Hg levels have been shown to produce 37% fewer fledged young. Consistent with how environmental Hg levels vary according to hydrological and biogeochemical factors, loon territories at high risk are found throughout New Hampshire. However, a grouping of loon territories at high risk in southeastern New Hampshire indicates greater than average methylmercury bioavailability. Two of these lakes, Swain's and Mendums, have loon egg and blood Hg levels higher than any other egg or breeding loon in the United States (based on 571 egg and 2,279 blood samples). This translates to a risk for southern New Hampshire populations of at least 32%, while in the southeastern study area the risk is 89%. Based on the 266 southern New Hampshire samples, ArcView 8.1 spatial analyst extension was used to model the potential extent of Hg risk to loons and relate the distribution of this exposure to major sources of Hg emissions in southern New Hampshire. Results from this coarse approach agree with earlier U.S. Environmental Protection Agency predictions and current weight of evidence strongly indicates that local, major emission sources in southern New Hampshire are related to high Hg levels in loons and are thereby enhancing Hg bioavailability in some areas of south-central and southeastern New Hampshire, as well as southern Maine. Further sampling efforts will provide higher resolution data, and ongoing efforts to link the relationship of Hg to population level impacts will provide the information needed to monetize the overall injury to loons and potentially other wildlife.