Man-made impoundment-induced transformation of river biota leads to profound and irreversible changes in the hydrological regime, the structure of communities of all groups of aquatic organisms, from phytoplankton to fish and their parasites. The transformation of river communities following impoundment is accompanied by intensive eutrophication. Due to this fact, the role of zooplankton in the fish diet grows, and stable foci of helminthiases form. One typical example is the fish and human diphyllobothriasis caused by cestodes Dibothriocephalus latus (Linnaeus, 1758) Luhe, 1899 (syn. Diphyllobothrium latum). The conditions in which the diphyllobothriasis pesthole has originated and developed are considered using the regulation of the Yenisei River and creation of Krasnoyarskoye storage reservoir as the example. D. latus plerocercoids were found in three species from the reservoir: perch, ruffe and pike, acting as second intermediate hosts, the primary role belonging to the perch, and to a smaller degree to the ruffe. Perch of both younger (2 +, 3+, 4+ years) and older age groups (5+ and older) are infected with plerocercoids due to the prevalence of plankton in their diet. A zonal pattern was observed in the plerocercoid infection in perch. The highest prevalence and mean abundance of helminthes were recorded from the fish living in the upper reaches, where habitats with shallow bays prevail; the infection rate in perch from in the middle and lower parts of the reservoir was somewhat lower.