As ecosystem engineers, North American beaver (Castor canadensis) punctuate stream continua over space and time through the construction of dams that retain water in open-meadow habitats. Such dams undergo natural assembly and disassembly with changes in intensity of beaver activity over time, which has the potential to alter nutrient and contaminant pathways in stream food webs. Here, we explored the nutritional quality (polyunsaturated fatty acid PUFA content) and mercury load (total mercury THg and methylmercury MeHg) of predatory aquatic insects in beaver-engineered stream habitats in the New York Adirondacks (USA). We hypothesized that (1) predatory insects inhabiting beaver-impounded sites would exhibit elevated Hg content, in line with the “reservoir effect,” but that this effect would decline with impoundment age and successional stage, and (2) that predatory insect PUFA content would be highest above beaver dams, given favorable growing conditions for algae in open-canopy meadows. We collected predatory aquatic insects representing the orders Odonata, Megaloptera, and Plecoptera from stream transects located above and below beaver-impounded areas representing the following dam conditions: intact dam (East Creek), recently breached dam (Sucker Brook), and dam absent, having breached >10 years prior (Chair Rock Creek). Insect samples were freeze-dried, homogenized using a mortar and pestle, and analyzed to obtain THg, MeHg, and PUFA concentrations. Preliminary results from our case study suggest that aquatic insects collected from meadowed, beaver-impounded areas had overall higher %MeHg (mean ± SD = 92 ± 8%) than aquatic insects collected in forested reaches immediately downstream (76 ± 17%). Conversely, PUFA concentrations of predatory insects were lower in beaver impounded sites (range = 0–50 ng/gdw) than in downstream forested reaches (range = 10–750 mg/gdw), with non-detectable levels of eicosapentaenoic acid (EPA) in most insects collected upstream of beaver impoundments. Together, these preliminary results postulate the role of beaver in altering not only stream habitats, but also the nutrient and contaminant dynamics of stream food webs, with further implications for terrestrial consumers of emergent aquatic insect prey. Overall, this research highlights the potential influence of ecosystem engineers on broader food web processes.