Lake Ladoga (Лáдожское Óзеро, Ladozhskoye Ozero; Laatokka) is a freshwater lake located in Republic of Karelia and Leningrad Oblast in northwestern Russia, not far from Saint Petersburg. It is the largest lake in Europe, and the 14th largest lake by area in the world.
The lake's area is 17,891 km² (excluding the islands). Its length (north to south) is 219 km, average width is 83 km, average depth is 51 m, maximum depth is about 230 m (in the north-western part). Basin area: 276,000 km², volume: 837 km³ (earlier estimated as 908 km³);. There are about 660 islands, with a total area of 435 km². Ladoga's level above the sea is 5 m on average. Most of the islands, including the famous Valaam archipelago, Kilpola and Konevets, are situated in the north-western part.
Lake Ladoga is navigable, being a part of the Volga-Baltic Waterway connecting the Baltic Sea with the Volga River. The Ladoga Canal bypasses the lake in the southern part, connecting the Neva to the Svir.
The basin of Lake Ladoga includes about 50,000 lakes and 3,500 rivers longer than 10 km. About 85% of the water income is due to tributaries, 13% is due to precipitation, and 2% is due to underground waters.
Deglaciation following the Weichsel glaciation took place in the Lake Ladoga basin between 12,500 and 11,500 radiocarbon years BP. Lake Ladoga was initially part of the Baltic Ice Lake (70-80 m. above present sea-level), a historical freshwater stage of Baltic Sea. It is possible, though not certain, that Ladoga was isolated from it during regression of the subsequent Yoldia Sea brackish stage (10,200-9,500 BP). The isolation threshold should be at Heinjoki to the east of Vyborg, where the Baltic Sea and Ladoga were connected by a strait or a river outlet at least until the formation of the River Neva, and possibly even much later, until 12th century AD or so.
At 9,500 BP, Lake Onega, previously draining into the White Sea, started emptying into Ladoga via the River Svir. Between 9,500 and 9,100 BP, during the transgression of Ancylus Lake, the next freshwater stage of the Baltic, Ladoga certainly became part of it, even if they hadn't been connected immediately before. During the Ancylus Lake subsequent regression, around 8,800 BP Ladoga became isolated.
Ladoga slowly transgressed in its southern part due to uplift of the Baltic Shield in the north. It was hypothesized, but not proven, that waters of the Litorina Sea, the next brackish-water stage of the Baltic, occasionally invaded Ladoga between 7,000 and 5,000 BP. Around 5,000 BP the waters of the Saimaa Lake penetrated Salpausselkä and formed a new outlet, River Vuoksi, entering Lake Ladoga in the northwestern corner and raising its level by 1-2 m.
The River Neva originated when the Ladoga waters at last broke through the threshold at Porogi into the lower portions of Izhora River, then a tributary of the Gulf of Finland, between 4,000 and 2,000 BP. According to some new data, it happened at 3,100 radiocarbon years BP (3,410-3,250 calendar years BP).
The Ladoga is rich with fish. 48 forms (species and infraspecific taxa) of fish have been encountered in the lake, including roach, carp bream, zander, European perch, ruffe, endemic variety of smelt, two varieties of Coregonus albula (vendace), eight varieties of Coregonus lavaretus, a number of other Salmonidae as well as, albeit rarely, endangered European sea sturgeon. Commercial fishing was once a major industry but has been hurt by overfishing. After the war, between 1945 – 1954, the total annual catch increased and reached a maximum of 4,900 tonnes. However, unbalanced fishery led to the drastic decrease of catch in 1955 – 1963, sometimes to 1,600 tonnes per year. Trawling has been forbidden in Lake Ladoga since 1956 and some other restrictions were imposed. The situation gradually recovered, and in 1971-1990 the catch ranged between 4,900 and 6,900 tonnes per year, about the same level as the total catch in 1938. Fish farms and recreational fishing are developing.
Since the beginning of the 1960s Ladoga has become considerably eutrophicated.
In the Middle Ages, the lake formed a vital part of the Trade Route from the Varangians to the Greeks, with the Norse emporium at Staraya Ladoga defending the mouth of the Volkhov since the 8th century. In the course of the Swedish-Novgorodian Wars, the area was disputed between the Novgorod Republic and Sweden. In the early 14th century, the fortresses of Korela (Kexholm) and Oreshek (Nöteborg) were established along the banks of the lake.
The ancient Valaam Monastery was founded on the island of Valaam, the largest in Lake Ladoga, abandoned between 1611 – 1715, magnificently restored in the 18th century, and evacuated to Finland during the Winter War in 1940. In 1989 the monastic activities in the Valaam were resumed. Other historic cloisters in the vicinity are the Konevets Monastery, which sits on the Konevets island, and the Alexander-Svirsky Monastery, which preserves fine samples of medieval Muscovite architecture.
During the Ingrian War, a fraction of the Ladoga coast was occupied by Sweden. In 1617, by the Treaty of Stolbovo, the northern and western coast was ceded by Russia to Sweden. In 1721, after the Great Northern War, it was restituted to Russia by the Treaty of Nystad. Later, in 1812 – 1940 the lake was shared between Finland and Russia. According to the conditions of the 1920 Tartu Peace Treaty militarization of the lake was severely restricted. However, both Soviet Russia and Finland had flotillas in Ladoga (see also Finnish Ladoga Naval Detachment). After the Winter War (1939-1940) according to the Moscow Peace Treaty, Ladoga, previously shared with Finland, became an internal basin of the Soviet Union.
During the Continuation War (1941-1944) not only Finnish and Soviet, but also German and Italian (see also Naval Detachment K and Regia Marina#Lake Ladoga) vessels operated there. Under these circumstances, during much of the Siege of Leningrad (1941 – 1944), Lake Ladoga provided the only access to the besieged city because a section of the eastern shore remained in Soviet hands. Supplies were transported into Leningrad with trucks on winter roads over the ice, the "Road of Life", and by boat in the summer. After World War II, Finland lost the Karelia region to the USSR, and all Finnish citizens were evacuated from the ceded territory. Ladoga became an internal Soviet basin. The northern shore, Ladoga Karelia with the town of Sortavala, is now part of the Republic of Karelia. The western shore, Karelian Isthmus, became part of Leningrad Oblast.