The article presents the results of comprehensive studies of the current state of terrestrial and aquatic ecosystems in southeastern Yakutia, with the Ust-Maisky District of the Republic of Sakha (Yakutia) as the case study. The soil cover of the study area is characterized by vertical zonality with a predominance of permafrost Leptosols and Podzols, and high heavy metal concentrations, exceeding health standards, including elements of the first hazard class: mercury, zinc, and lead. The surface waters of watercourses surveyed in this area feature a low total dissolved solids content, neutral to weakly alkaline pH, and a predominance of bicarbonates, calcium, and magnesium in their ionic composition. Iron, copper, aluminum, and mercury levels in the water exceeded maximum permissible concentrations for fishery waterbodies, not only due to the natural features of the area but also under the mining impact. Industry-generated water in the tailings dumps at the villages of Allah-Yun and Zvezdochka contained elevated levels of lead, mercury, and cadmium. Analysis of bottom sediments revealed local accumulation of manganese, zinc, lead, and cobalt in natural watercourses, as well as mercury in man-made water bodies. In this context, the zooplankton community was found to be inhibited. In general, this area requires long-term monitoring to assess the pollution sources and their impact on the ecosystems. Particular attention should be given to abandoned hydraulic engineering facilities in the villages of Allah- Yun and Zvezdochka, with a recommendation to include them in the State Register of Accumulated Environmental Damage in order to develop measures to reduce environmental risks.