Аннотация:Samples of marsh frogs (Pelophylax ridibundus) were collected from two thermal reservoirs in thesoutheastern part of the Kamchatka Peninsula: (1) from a discharge channel of Thermal Power Plant #2, Petropavlovsk-Kamchatsky (hereinafter TPP); and (2) from thermal waste waters of the Township of Paratunka (hereinafter Paratunka). The concentrations of iron and manganese in the TPP waters are higher than in Paratunka by 7 and 1.2 times, respectively; while the concentrations of cobalt, copper, and nickel in the TPP waters are lower in comparison with Paratunka. The striata and hemimaculata phenetic morphs predominate in the Paratunka population; while maculated (maculata), white-throated (albicollis), and white-bellied (albiventris) individuals predominate in the TPP population. Both males and females in the TPP population feature higher average age, body length, body weight, and postmetamorphic growth rate values in comparisonwith the Paratunka population. Males in the TPP population feature a significantly higher relative testes mass, which can be a compensatory reaction to the complex of pollutants. For the first time, the predominance of erythrocytes with attached micronuclei was identified in marsh frog populations of Kamchatka, which indicates chromosomal aberrations induced by mutagens present in the aquatic environment. Sexualdifferences in the proportion of erythrocytes with attached micronuclei have been identified in frogs of the Paratunka population, which indicates a higher mutation frequency in erythrocytes of males in comparison with females. The proportion of micronuclei increases in erythrocytes of older individuals; apparently, this is due to the cumulative effect of xenobiotics present in the aquatic environment. The morphophysiological indices (i.e., relative masses) of organs make the highest relative contribution to the total variance of the set of characteristics studied in marsh frogs belonging to two different populations; while cytogenetic disordersin somatic cells identified by the micronucleus test make the greatest difference in sexual differences (Paratunka population only).