In partnership with over 40 national parks across the U.S., we are developing the use of dragonfly nymphs as bio-sentinels for mercury (Hg) in aquatic foodwebs. To validate the use of these sentinels, and gain a better understanding of the connection between biotic and abiotic pools of Hg, this project also includes collection of landcover/landscape data, surface water chemistry including Hg and Hg-relevant chemistry (pH, sulfate, dissolved organic carbon (DOC)), and most recently, sediment Hg. Because of the wide geographic scope of the research, the project also provides a nationwide snapshot of Hg in these diverse media, primarily in undeveloped watersheds. In preliminary data from 23 parks sampled in 2013 total Hg (THg) in water ranged over two orders of magnitude (0.16-28 ng/L; median=2.2 ng/L), and pH ranged from 5.5-9.2 (mean=7.7).  In dragonfly nymphs, THg concentrations averaged 154 ± 124 (mean ± SD) ppb, dw. THg in surface water was weakly correlated with THg in dragonfly nymphs (Pearson’s R=0.38). Sites with the greatest THg concentrations were located in New England as well as western sites that could be influenced by global Hg sources as well as regional to local influences such as volcanic activity, wildfires, and urbanization. Whereas dragonfly and water THg concentrations were generally greater in the eastern compared to the western U.S. in 2012, based on data from a smaller set of 12 pilot parks, the addition of parks that provide better coverage of western states has changed the geographic pattern of Hg in water and biota. Site-to-site variability within a park was high; one park included a site with the greatest concentrations of THg in dragonflies and fourth-highest concentration of THg in water, but also a site where dragonfly THg fell in the lowest quartile of all the data. Our ongoing research is examining the factors that influence water and dragonfly Hg, as well as sample collection across a broader set of parks (47 in 2014), and evaluation of temporal trends in dragonfly and water Hg within a project year.