Abstract— <p>Located on the eastern coast of Lake Baikal, Lake Kotokel is one of the largest in the Baikal region and of great fishing and recreational importance. The first ever detailed study of the Lake Kotokel sediments has provided an extensive set of data on spatial as well as quantitative distribution of metals. A series has been constructed illustrating metal accumulation in the Kotokel sediments: Fe &gt; Na &gt; Mn &gt; K ≥ Ca &gt; Mg &gt; Zn&#xa0;&gt; Cr &gt; Co ≥ Cu &gt; Ni &gt; Pb &gt; Cd. Seasonal dynamics was found to be typical only for K, Na, Mg, Cr, and Co. An analysis of the spatial distribution of heavy metals over the water area showed that extreme concentrations were most often observed in areas of faults of the northeastern strike and were probably associated with the discharge of fracture–vein waters. Silty sediments with a high organic carbon content in central and southern parts of the lake are characterized by the accumulation of Cu and, to a lesser extent, Ni. Correlation analysis showed a positive relationship of different intensity for all the heavy metals studied, both with each other and with organic carbon and silty and pelitic fractions of the sediments. For the first time, an assessment was made of the extent of contamination of bottom sediments with heavy metals and the associated environmental risk for the Kotokel Lake. The values of the geoaccumulation index, the enrichment factor, and the potential environmental risk index indicated the predominantly background levels of heavy metals, while local enrichment in Mn, Zn, Cu, and Co did not exceed a moderate level, suggesting that there was no danger to aquatic organisms. The study will be helpful in developing recommendations on the hydroecological safety of the reservoir, as well as for assessing the quality of lake sapropel as a potential raw material.</p>