Atmospheric deposition of inorganic mercury (Hg) is increasing in the western U.S. largely due to global sources. Once deposited on the landscape, inorganic Hg can be transported to wetland environments where bacteria transform it into methylmercury (MeHg), a bioaccumulating neurotoxin. This is a particular concern in mountain environments, where beaver populations are increasing. Beavers change river corridors by creating wetland environments that can be hotspots for MeHg production. Previous studies have measured elevated MeHg concentrations in water from beaver ponds. The objective of this study is to expand on previous research to determine (1) the concentrations of MeHg in different parts of the river corridor (sediment and surface water) where beavers are active, and (2) the main drivers of MeHg production. We sampled sediment and surface water at two sites in Crested Butte (CB), CO and Manitou Experimental Forest Observatory (MEFO), CO. Two ponds were sampled at each site separated by age class (old and young). Each pond is further segmented into four eco-geomorphic units (EGU, areas with unique landscape characteristics) that we predicted would have varied Hg concentrations: stream, pond, inundated vegetation, and dry vegetation. We hypothesized that the young beaver ponds and the inundated vegetation EGU would have higher concentrations of MeHg in both water and sediment because these areas have greater fresh carbon inputs—a necessary substrate for Hg methylation. MeHg concentrations were significantly higher in young versus old pond sediment at CB (mean = 5.5 ng g_1, p = 0.045) but there was no significant difference between pond sediment ages at MEFO (p > 0.05). Dry vegetation areas, which are periodically inundated, had the highest MeHg concentrations at both sites (mean = 3.1 ng g-1, p > 0.05). In water, inundated vegetation at MEFO was elevated compared to the pond (mean = 0.006 ng L-1, p > 0.05). These results contradict our hypotheses; they indicate that areas experiencing wetting and drying cycles and old ponds accumulating MeHg through time lead to the highest MeHg concentrations in beaver-active rivers. Although concentrations in sediment are high compared to other unpolluted areas, water concentrations are below the EPA threshold of 2 ppb MeHg, suggesting that despite being a hotspot for MeHg production, concentrations are not of concern and do not pose a threat to drinking water sources for downstream communities.