Water quality in the Modonkul’ River, flowing in a territory with mining industry, is considered. The analyzed data characterize the period 2019–2021. The assessment of pollution or the parameterization of water quality were carried out using the universal combinatory index of water pollution. In the upper reaches of the Modonkyl’ River, the water chemistry is of hydrocarbonate calcium type. In the zone of mixing of river and mine waters, the water chemistry changes to sulfate, mostly, sodium-calcium-magnesium type. The general regularity in the behavior of microelements in the Modonkul’ R. water is an increase in their concentration at an increase in TDS. Downstream the river, the concentrations of heavy metals increase: Cu, Zn, Pb by 1.1–1.4 times; Mn, Co, As by 6.6–11 times; and Cd, by 8 times. In the upper reaches of the river, its water quality was classified as weakly polluted, 2nd class. Further downstream, the water is classified as dirty, 4th class with a decrease in the subclass from a to b.

Lake Gusinoe is the second largest freshwater lake in Transbaikalia. Lakes serve as a source for drinking water, irrigation, and as a water source for the electricity, aquatic production, and tourism industry. Currently variations of content nutrients and organic matter differ in different areas of the lake. The content of total nitrogen, phosphorus, organic matter, and dissolved oxygen are distinguished more than 1.2–2.0 times. In accordance with the behavior of elements in the water, three groups of elements can be distinguished. The first group of elements, including Li, Ga, Ge, As, Rb, Sr, Mo, Cd, W, and U, were directly correlated with variations of major elements. The first group of elements showed decreasing concentrations with an increasing amount of total dissolved salt (TDS). The second group of elements, including Fe, Y, Nb, Th, and REE, were correlated oppositely with variations of TDS. The behavior of the third group of elements, including Mn, Zn, Ni, Cu, and Pb, decoupled with TDS. The value of the Eu anomaly was positively correlated with TDS. The water of Lake Gusinoe was extremely enriched by W, Mo, V, U, Li, Sr, and Ga; moderately by Ni, Cu, Ge, As, Rb, Cd, and Pb; and minimally by Al, Cr, Mn, Fe, Co, Zn, Y, Th, and REE.