The long-term changes in the structure of phytoplankton in two large lakes of northwestern Russia-Onega and Imandra-are considered. Similar regularities in anthropogenic changes in the phytoplankton communities are found in both lakes. Despite the local nature of the lakes' pollution, phytoplankton changes are traced within several tens of kilometers from the sources of wastewater discharge. The mass species of algae that are characteristic of the regions subjected to human impact are identified in both lakes.