Bothnian Sea in the context of "Rauma, Finland"

The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North and Central European Plain regions. It is the world's largest brackish water basin.

The sea stretches from 53°N to 66°N latitude and from 10°E to 30°E longitude. It is a shelf sea and marginal sea of the Atlantic with limited water exchange between the two, making it an inland sea. The Baltic Sea drains through the Danish straits into the Kattegat by way of the Øresund, Great Belt and Little Belt. It includes the Gulf of Bothnia (divided into the Bothnian Bay and the Bothnian Sea), the Gulf of Finland, the Gulf of Riga and the Bay of Gdańsk.

The Gulf of Bothnia (/ˈbɒθniə/, Swedish: Bottniska viken, Finnish and Meänkieli: Pohjanlahti) is divided into the Bothnian Bay, the (North) Kvarken and the Bothnian Sea, and it is the northernmost arm of the Baltic Sea, between Finland's west coast (Ostrobothnia (East Bothnia)) and the northern part of Sweden's east coast (Västerbotten (Westrobothnia, West Bothnia) and Norrbotten (North Bothnia)). In the south of the gulf lies Åland, between the Sea of Åland and the Archipelago Sea.

Kvarken (Swedish: Kvarken, Norra Kvarken (as opposed to South Kvarken); Finnish: Merenkurkku, lit. 'throat of the sea') is the narrow region of the Gulf of Bothnia separating the Bothnian Bay (the inner part of the gulf) from the Bothnian Sea. The distance from the Swedish mainland to the Finnish mainland is around 80 km (50 mi), while the distance between the outermost islands is only 25 km (16 mi). The water depth in the Kvarken region is only around 25 metres (82 ft). The region also has an unusual rate of land rising at almost 10 mm (0.39 inches) a year.

Several attempts to cross the strait swimming have been made, but cold water and currents have usually been insurmountable obstacles. The first successful crossing was carried out by Lennart Flygare, Pavio Grzelewski and Tore Klingberg, who on 24 July, 2018, swam from Valassaaret (Valsörarna) on the Finnish side to Holmöarna in Sweden. It took them 12 hours 2 minutes to cross the strait.

Ostrobothnia (Swedish: Österbotten; Finnish: Pohjanmaa) is a historical province comprising a large portion of western and northern Finland. Before the Treaty of Fredrikshamn in 1809, Ostrobothnia was part of Sweden. It is bounded by Karelia, Savo, Tavastia (Häme) and Satakunta in the south, the Bothnian Sea, Bothnian Bay and Swedish Norrbotten in the west, Lapland in the north and Russia in the east.

The Åland Sea (or the Sea of Åland; Swedish: Ålands hav, Finnish: Ahvenanmeri) is a waterway in the southern Gulf of Bothnia, between Åland and Sweden. It connects the Bothnian Sea with the Baltic Sea proper. The western part of the basin is in Swedish territorial waters while the eastern part is in Finnish territorial waters.

The Åland Sea has two sub-basins. The main basin is the Åland Sea proper, also called the northern Åland Sea basin. In the south, there is the smaller Lågskär Deep, also called the Lågskär Basin or the southern Åland Sea basin. The narrowest part on the northern edge of the basin is named the Southern Quark or South Kvarken (Swedish: Södra Kvarken, Finnish: Ahvenanrauma). The trench running on the bottom of the Sea of Åland contains the second-deepest spot of the Baltic Sea, at a depth of 301 meters, which is second only to Landsort Deep. The mean depth of Åland Sea is 75 m, area 5,477 km and its volume is 411 km. The Archipelago Sea and the Åland Sea regulate water exchange between Gulf of Bothnia and Baltic Proper.

South Kvarken (Finnish: Ahvenanrauma, Swedish: Södra Kvarken) is the narrowest stretch of sea between Finnish Åland and Sweden, forming a strait connecting the Sea of Åland and the Bothnian Sea of approximately 30 km (18.5 mi) across.

60°08′57″N 19°10′21″E / 60.1492°N 19.1725°E / 60.1492; 19.1725