These data were collected as part of the Southwest Alaska Inventory and Monitoring Network (SWAN) freshwater contaminants protocol. The protocol outlines a framework for monitoring mercury (Hg) concentrations in resident lake fish within SWAN parks. The primary goal of this monitoring is to understand the spatial differences, temporal trends, and health ramifications of Hg contamination in resident lake fish. Monitoring relies on total Hg in fish axial muscle as an indicator of methyl Hg exposure. It targets four high-priority lakes which vary in size, depth, wetland cover, glacial influence, and Hg concentration. These lakes are located in two parks: Lake Clark National Park and Preserve (LACL) and Katmai National Park and Preserve (KATM). The focal species is lake trout (Salvelinus namaycush), a widespread, long lived, top predator in SWAN lakes. However, if other species are sampled as bycatch, they may be retained and analyzed if they represent species-specific data gaps in Hg concentration. Two broad types of data are generated from this protocol. The first type includes observations and measurements that are recorded while sampling and processing fish (e.g., length, weight, gender). The second type includes results of analyses performed by contract laboratories (e.g., age, total Hg). This particular dataset includes those two broad types of data for 49 fish sampled in 2019 and 2020 from 2 lakes in LACL: Lake Clark and Kijik Lake. Of those 49 fish, 40 were lake trout, 6 were burbot (Lota lota), 2 were Arctic grayling (Thymallus arcticus), and 1 was Arctic char (Salvelinus alpinus).