A connection between the dynamics of the distribution of macrophytes in lakes isolated from a large lake or sea with changes in the coastlines of large reservoirs has been established. In the process, there are a change in the composition of macrophytes or their decrease at different stages in the coastlines change of lakes and seas. The conclusions were based on a multi-proxy paleolimnological study of the Lake Ladoga’ island lakes and lakes of the Kurgalsky Peninsula on the Gulf of Finland southern coast of the of the Baltic Sea. © Author(s) 2024.