geographer and zoologist who established the foundations of limnology in Russia with his systematic studies on the physical, chemical, and biological conditions of fresh waters, particularly of lakes. Important, too, was his work in ichthyology, which yielded much useful data on the paleontology, anatomy, and embryology of fishes in Russia. Of broader significance were Berg's findings on the periodicity of reproduction among fishes and the influence of climatic variations on migratory species. He is also credited with having discovered the symbiotic relationship between lampreys and salmon.

Berg extended his ichthyological research to zoogeography, a field of study concerned with the distribution of animals. Data from his zoogeographic analyses enabled him to reconstruct with considerable accuracy the chronology of the major glaciations. In turn, he used these paleoclimatological reconstructions to investigate the origin of various sedimentary rocks and the formation of soils, the results of which demonstrated the efficacy of integrating the procedures of modern geography and historical geology.