Methylmercury (MeHg) bioaccumulation in freshwater aquatic systems is impacted by anthropogenic stressors, including climate change and excess nutrients. The goal of this study was to determine how warmer water temperatures and excess nutrients would impact zooplankton communities and phytoplankton concentrations, and in turn increase or decrease MeHg concentrations in freshwater zooplankton. I used a 2x2 factorial design to determine if the interaction of temperature and nutrients would impact plankton metrics and zooplankton MeHg concentrations. Mesocosms were filled with Hg-contaminated water and plankton from Cottage Grove Reservoir, Oregon, a waterbody that has experienced decades of elevated MeHg concentrations and corresponding fish consumption advisories due to run-off from Black Butte Mine tailings, located within the watershed. Treatment combinations of warmer temperature (increased by 0.5°C) and nutrient addition (a single pulse of excess nitrogen and phosphorous), control, and a combination of temperature and nutrients were applied to mesocosms. While plankton did respond to treatments, zooplankton biomass and phytoplankton concentrations did not have significant relationships to MeHg concentrations. However, a significant interactive effect of nutrients and temperature was present: nutrients appeared to buffer against increased MeHg concentrations when temperature was elevated. The mechanisms for this interaction appear to be related to a shift to larger body size and an increase in abundance of Daphnia over copepods. Findings suggest that community composition and species-specific differences in both zooplankton and phytoplankton could play a role in MeHg transfer to higher trophic levels.