The article contains the results of a study of the ecological hazards of long-term consequences (XVII-XXI centuries) of human activities on the shores and waters of the South-Eastern Baltic Sea. The following issues have been considered: 1) territorial losses and the destruction of man-made objects; 2) natural radioactivity of the potential source of mineral raw materials — titanium-zirconium concentrates in beach sands and their content of 137Cs (the “Chernobyl trace”); 3) echoes of the Great Patriotic War (WWII) — ammunition on the shore and dumping on the seabed of captured chemical warfare agents from the arsenal of Nazi Germany. The study has determined the following. Coast in Courland, after Peter the Great built the port of Libava (the end of XVII century) and after malls were extended in the nineteenth century, had been stable. Modernization of the military avantport of Emperor Alexander III at the beginning of the XX century with the removal of the sea piers on 2123 m caused the obstruction of sands along the coast and its grassroots catastrophic erosion to the North of the port. By the 1930s, the bottom sands have been eroded to Cape Akmenrags (along with the coast to ~40 km, the volume of >70 million m3). By the 1990s, at 4-6 km closest to port, the shore has receded up to 200 meters. Houses, landfills, fragments of the sewer were destroyed. There was a threat of collapse of toxic objects of municipal wastewater treatment facilities into the sea (sludge beds, chlorination station, town Schedes). An environmental disaster was prevented by the timely constructed shore protection facilities (1988-1991). The erosion of the shore caused the accumulations on the beach of industrially important titanium-zirconium concentrates (>1,5 t/m3). Heavy minerals (zircon, monazite, etc.) contain natural radionuclides (thorium, uranium etc.), their activity (5668,6 Bq/kg) exceeded the hygienic standard (1500 Bq/kg) by ~4 times. Mineral raw materials of this quality refer to the IV class of hazard. As for 137Cs, considering the period from the Chernobyl disaster (April 1986) to the analysis of the specimens (spring 2015 ~the half-life of the isotope), the concentration could reach,: in sands — 110 Bq/kg, in organic soils and peatlands — up to 500 Bq/kg. The contamination was consistent with the radiation condition of the several territories of the USSR, which have experienced the impact of the disaster, but was higher than in the Altai (“Semipalatinsk trace”, 41-43 Bq/kg). Echoes of the War resulted in storms bringing ashore ammunition, which caused injuries and deaths of adolescents, who found such “waste” of World War II (the town Schedes, the elimination of the Nazis in “Liepaja port”, 1945). In the deep (92-208 m) basins (Bornholm, Gotland) and in other areas of the Baltic Sea there are about 60 underwater dumpings of chemical warfare agents. The threat of environmental disaster may appear in the case of their large-scale mechanical damage (trawling, drilling, pipelines, etc.). The uncertainty of the information about the number of dumpings of chemical warfare agents keeps a danger of their location on the coast and bringing by waves to the beach. Further exploration and monitoring of dumpings are particularly relevant in connection with the laying of the gas pipeline “Nord stream – 2”.