This data release includes organic and mercury data for biologic samples collected from two studies conducted in the Niagara River Area of Concern (AOC) and the Buffalo River AOC during 2020. The first, Niagara River Forage Fish study assessed contaminant data from 26 fish-tissue samples collected at four locations in or near the Niagara River AOC during 2020, and from two reference material samples. More than 160 polychlorinated biphenyls (PCBs) congeners were analyzed in 21 fish-tissue samples and in one reference material sample. Dioxins and furans were analyzed in five fish-tissue samples and in a second reference material sample. Percent lipid and percent moisture were analyzed in all 26 fish-tissue samples. The second, Buffalo River Lumbriculus study analyzed concentrations of over 160 PCB congeners and total mercury in batches of Lumbriculus variegatus (Oligochaete) which had been exposed for 28 days (in a laboratory) to sediments collected from 15 sites in the Buffalo River AOC during 2020. This data release also compiles laboratory quality assurance information, including sample replicates, laboratory blank data, laboratory spike data, matrix spike recoveries, and replicate matrix spike recoveries that were associated with these samples.