Lake Ladoga

Under Lake Ladoga, two kinds of ground meet.

Long ago, ice helped scoop out its basin.

Lake Ladoga sits on a boundary between two kinds of ground: the crystalline rock of the Baltic Shield and the Great Russian Plain. The International Association for Great Lakes Research lists its origin as both glacial scouring and tectonic uplift.

Scientists list several small invertebrates in the lake as relict species, and the Ladoga ringed seal itself is called a relic from the glacial era.

ILEC describes Lake Ladoga as lying on the borderline between the crystalline Baltic Shield and the Great Russian Plain, with a complicated geological history in its 250,600 km² drainage basin; the differences show in the structure of its shores and depressions. IAGLR's lake profile gives its geologic origin as glacial scour and tectonic uplift.

The lake floor is lined with seven sediment types, from boulders and gravel near shore to clayey silt in the deepest areas. ILEC lists relict invertebrates, among them Pontoporeia affinis, Pallasea quadrispinosa, Mysis relicta and Mesidothea entomon, and the Marine Mammal Protected Areas Task Force calls the Ladoga ringed seal a relic from the glacial era.

In the north of the lake there are hundreds of rocky islands.

Some have steep rock walls.

Along the lake's northern part, long, narrow bays, straits and hundreds of islands make a maze of water and rock. Some of the highest islands have steep walls that rise up to 80 meters.

At the end of 2017, Russia decided to set up the Lake Ladoga National Park here. It covers about 122,000 hectares, with almost a hundred small lakes and nearly 1,000 kilometers of shoreline with no buildings.

According to a 2018 press release from Finland's Ministry of the Environment, the Finnish Environment Institute and Metsähallitus, Russia decided at the end of 2017 to establish a national park in the Lake Ladoga archipelago. It covers about 122,000 hectares in the Lakhdenpokhya, Sortavala and Pitkyaranta municipalities of the Republic of Karelia: a network of long, narrow fjord-like bays, straits and islands, the highest 'reef islands' rising to 80 m, with hundreds of islands, almost a hundred small lakes and nearly 1,000 km of unbuilt shoreline.

The release describes diverse tree stands including old-growth forest with many threatened and rare species, and a viable population of the Ladoga ringed seal.

The Ladoga ringed seal lives only in this lake.

In late winter, mother seals have pups in snow dens on the ice.

The Ladoga ringed seal lives in fresh water and is found only in Lake Ladoga. There are about 6,000 of them, and the IUCN lists the subspecies as Vulnerable.

The seals need ice. Mothers give birth in late February and early March in dens dug into snowdrifts on the ice. In summer, some seals rest on islands. The lake also has 46 kinds of fish.

The Marine Mammal Protected Areas Task Force's Lake Ladoga IMMA factsheet describes Pusa hispida ladogensis as endemic to the lake, listed as Vulnerable (A2b) by the IUCN (Sipilä 2016), with a population of roughly 6,000, 13-49% fewer than in the mid-20th century. The seals breed on ice, giving birth in late February and early March in snow lairs on fast ice; about 80% breed in the central lake and 20% in the northern skerries. In summer they haul out on islands such as the Valaam and Zapadnyi archipelagos. Threats named include climate change, by-catch in fishing gear, recreation and industrial development.

ILEC lists 46 fish species, including Coregonus lavaretus, Osmerus eperlanus, Perca fluviatilis and Salmo salar.

The lake water is cold. Wear a life jacket in a boat.

If you see a seal, stay far away and watch quietly.

Cold water can be dangerous even on a sunny day. The US National Weather Service explains that falling into cold water can make you gasp and breathe fast, and that wearing a life jacket greatly improves your chances. The lake also gets big waves: one wave was measured at 5.8 meters high.

If you see seals, watch them from a safe and respectful distance and never approach or touch them, as NOAA Fisheries advises for seals and other marine animals.

ILEC records Lake Ladoga's highest measured wind wave at 5.8 m, with a length of 60 m. The US National Weather Service warns that cold shock can be as severe at 10-15 °C as at 2 °C, triggering gasping and rapid breathing in the first minutes, and that a life jacket significantly increases the chance of survival.

NOAA Fisheries asks people to view seals and other marine mammals from a safe and respectful distance, never approaching or touching them; the IMMA factsheet notes that fishermen on the ice have disrupted the Ladoga seals' behavior.