The goal of the paper is summarizing the results of the 20-years monitoring of the deposit sites of the dredged material in the Eastern Gulf of Finland (EGoF) and in the Neva Bay. The biotic and abiotic components of deposit sites ecosystems were observed there in 1999-2019, with using standard monitoring methods, in order to reveal effects of dumping on hydrobiologic communities and to determine their environmental status. The Biota Condition Index for 6 deposit sites was calculated and compared to areas which are not stressed by dumping. It is shown that the biological communities (especially - benthic) in the deposit sites areas are enormous not-sustainable and start their succession from the zero point every time after repeating stressing effect of dumping.