Baltic Sea

The Baltic Sea is an arm of the Atlantic Ocean surrounded 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, meaning it contains a mix of fresh and salt water.

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, making it almost like 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 several important areas such as 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 "Baltic Proper" is bordered on its northern edge by Åland and the Gulf of Bothnia, on its northeastern edge by the Gulf of Finland, on its eastern edge by the Gulf of Riga, and in the west by the Swedish part of the southern Scandinavian Peninsula.

The Baltic Sea is also connected by artificial waterways to the White Sea via the White Sea–Baltic Canal and to the German Bight of the North Sea via the Kiel Canal.

Definitions

Administration

The Helsinki Convention on the Protection of the Marine Environment of the Baltic Sea Area talks about the Baltic Sea and the Kattegat, but it doesn’t call Kattegat a part of the Baltic Sea. It says the "Baltic Sea Area" includes the Baltic Sea and the entrance to it, ending at a line in the Skagerrak at 57°44.43'N.

Traffic history

In the past, the Kingdom of Denmark made ships pay money called Sound Dues at three places: at Kronborg castle near Helsingør in the Øresund, at Nyborg in the Great Belt, and at its narrowest part near Fredericia in the Little Belt.

Oceanography

Experts say the border between the Baltic Sea and the North Sea is usually at the Langelandsbælt, the southern part of the Great Belt near Langeland, and the Drogden-Sill strait. The Drogden Sill is north of Køge Bugt and connects Dragør near Copenhagen to Malmö. It is where the Øresund Bridge is, including the Drogden Tunnel. With this border, the Danish Straits are part of the entrance, but the Bay of Mecklenburg and the Bay of Kiel are part of the Baltic Sea. Another common border is the line between Falsterbo in Sweden and Stevns Klint in Denmark.

Hydrography and biology

The Drogden Sill, which is only 7 meters deep, limits the flow into Øresund, and the Darss Sill, at 18 meters deep, limits the flow into the Belt Sea. These shallow areas make it hard for salty water from the Kattegat to reach places around Bornholm and Gotland.

The Kattegat and southwestern Baltic Sea have lots of oxygen and many kinds of plants and animals. The rest of the Baltic Sea has less salt, less oxygen, and fewer plants and animals.

Etymology and nomenclature

We do not know exactly how the Baltic Sea got its name. Long ago, writers used many different names. Some called it the Suebic Sea after a group of people, and others called it the Sarmatian Ocean. The name "Baltic Sea" was first used by a German writer in the eleventh century. He might have chosen this name because the sea runs through the land like a belt.

Other ideas about the name include links to words meaning “white” or “fair” in old languages, or words for “enclosed sea” or “bay.” During the Middle Ages, the sea had many names, but the name Baltic Sea became common after the year 1600. Today, many languages have their own names for the Baltic Sea, often based on where it is or how big it is.

History

Classical world

During the time of the Roman Empire, the Baltic Sea was called the Mare Suebicum or Mare Sarmaticum. Tacitus wrote about it in AD 98, calling it a brackish sea where ice would break apart in spring. The name came from the Suebi tribe. Later, Jordanes called it the Germanic Sea in his work, the Getica.

Middle Ages

In the early Middle Ages, Scandinavian traders built a big trading network around the Baltic. They also fought for control of the sea with tribes living on the southern shore. The Scandinavians used rivers in Russia to travel to the Black Sea and southern Russia. This time is known as the Viking Age.

Since then, the Scandinavians have called the Baltic Sea Austmarr, meaning "Eastern Sea". The lands around the Baltic's eastern shore were some of the last in Europe to become Christian. Finland was Christianized by Swedes in the twelfth century, and Estonia and Latvia in the early thirteenth century by Danes and Germans. The Teutonic Order controlled parts of the southern and eastern shore, and Lithuania was the last European country to adopt Christianity.

An arena of conflict

Between the 8th and 14th centuries, there was a lot of piracy around the Baltic coasts. In the 11th century, people from Germany began settling along the southern and eastern shores, a movement called the Ostsiedlung ("east settling"). Settlers also came from the Netherlands, Denmark, and Scotland.

Between the 13th and 17th centuries, the Baltic Sea was controlled by different countries at different times, including the Netherlands, Germany, Sweden, and Russia. In the 13th to 16th centuries, the Hanseatic League, a group of trading cities, was very powerful around the Baltic and the North Sea. In the sixteenth and early seventeenth centuries, Poland, Denmark, and Sweden fought for control over the sea.

In the eighteenth century, Russia and Prussia became the main powers over the Baltic Sea. Russia's Peter the Great founded his new capital, Saint Petersburg, near the Gulf of Finland. There was a lot of trading between the Baltic region and places like England and the Netherlands.

Since World War II

After World War II, many people had to leave their homes in areas east of the Oder-Neisse line. Poland took control of most of the southern shore, and the Soviet Union took over the Baltic states on the eastern shore.

Finland and Sweden joined NATO in 2023 and 2024, meaning the Baltic Sea is almost completely surrounded by NATO members. However, the sea remains open to all nations.

Storms and storm floods

Winter storms start in October and can cause big waves and shipwrecks. One famous shipwreck was the ferry MS Estonia in 1994. The cold and brackish water of the Baltic helps preserve old wooden ships, like the Vasa.

Big floods happen when the water level rises more than one meter above normal. There have been many floods over the years.

Geography

An arm of the North Atlantic Ocean, the Baltic Sea is surrounded by Sweden, Denmark, Finland, and the Baltic countries. It stretches about 1,600 km long and averages 193 km wide, with an average depth of 55 meters. The deepest point reaches 459 meters.

The Baltic Sea is one of the world's largest brackish water bodies. It was formed by glacial erosion during the last few ice ages. The sea's surface area covers around 349,644 km², and its volume is about 20,000 km³. It has roughly 8,000 km of coastline.

Geology

Main article: Geology of the Baltic Sea

The Baltic Sea looks a bit like a riverbed. It has two parts called the Gulf of Finland and the Gulf of Bothnia. Long ago, huge glaciers changed the land. They turned an old riverbed into the sea we see today.

The land around the Baltic Sea is still rising up. This happened because the weight of ice pressed it down. As the land rises, the sea's area and depth are slowly getting smaller. In some places, the land rises about eight millimeters every year. Old seabed is becoming new land.

Biology

Fauna and flora

See also: List of fish in Sweden

The Baltic Sea has many animals and plants. You can find sea fish like Atlantic cod, Atlantic herring, and European flounder. There are also freshwater fish such as European perch and northern pike. In some places, freshwater fish are more common.

The blue mussel is very common and is one of the most seen animals in the sea. Some special plants and animals live only in the Baltic Sea. There are also some older sea animals that stayed behind after a big freeze, long ago.

Cetaceans like the harbor porpoise live in the Baltic Sea, and sometimes bigger whales visit.

Environmental status

Every summer, green blooms cover parts of the sea. This happens because of extra nutrients from farms. Some parts of the sea floor have very little oxygen, making it hard for sea creatures to live there.

After World War II, old weapons were dropped into the sea. Experts say this can be risky for people living near the coast.

Future change

Climate change and pollution could change the Baltic Sea. Scientists worry the sea might start releasing carbon dioxide and methane into the air. The Baltic Sea has special features, like its mix of fresh and salty water. Future predictions include warmer air, more heavy rain, milder winters, warmer water, and rising sea levels. Some predictions are less certain.

Economy

See also: Baltic Sea cruiseferries, Ports of the Baltic Sea, and List of oil and gas fields of the Baltic Sea

The Baltic Sea helps many countries with trade, especially moving oil. People worry about oil spills because the sea’s water changes slowly. The area also has lots of tourists, and they worry about pollution like oil in the water. ^{[citation needed]}

Many ships are built in shipyards around the Baltic Sea. Big shipyards are in cities like Gdańsk, Gdynia, and Szczecin in Poland; Kiel in Germany; Karlskrona and Malmö in Sweden; Rauma, Turku, and Helsinki in Finland; Riga, Ventspils, and Liepāja in Latvia; Klaipėda in Lithuania; and Saint Petersburg in Russia. A big bridge between Denmark and Sweden was finished in the late 1990s, and a new tunnel between Denmark and Germany will be done in 2029. The Baltic Sea is also becoming a good place for wind energy, with plans for lots of offshore wind power by 2030.

Ferries

There are many ferries on the Baltic Sea that carry people and cargo. Some of these ferries are:

• Birka Gotland (cruises from Stockholm to Gotland and Åland Islands)
• Destination Gotland (Gotland-mainland Sweden)
• Eckerö Line (Estonia-Finland)
• Eckerö Linjen (Sweden-Åland Islands)
• Finnlines (Finland-Germany, Finland-Sweden, Germany-Sweden, Poland-Sweden)
• Polferries (Poland-Sweden, Poland-Denmark)
• Scandlines (Denmark-Germany)
• Stena Line (Denmark-Sweden, Germany-Sweden, Latvia-Sweden, Poland-Sweden)
• Tallink and Tallink Silja (Estonia-Finland, Estonia-Sweden, Finland-Sweden)
• TT-Line (Germany-Lithuania, Germany-Sweden, Lithuania-Sweden, Poland-Sweden)
• Unity Line (Poland-Sweden)
• Viking Line (Estonia-Finland, Finland-Sweden)
• Wasaline (Finland-Sweden)

Tourism

Critical Maritime Infrastructure (CMI)

Critical maritime infrastructure includes important systems like pipelines, ports, undersea cables, and energy installations. In recent years, these systems in the Baltic Sea have become more important politically. Some problems happened between 2022 and 2025, such as damage to important pipelines and cables. Because of this, groups like NATO and the European Union, as well as nearby countries, are working together to protect these systems better.

The Baltic Sea has also faced challenges from what are called "hybrid threats." These are actions that happen below the level of war but can still cause big problems. Protecting against these threats needs strong teamwork between different groups, but this can be difficult because of legal and responsibility issues.

Helsinki Convention

Main article: Helsinki Convention on the Protection of the Marine Environment of the Baltic Sea Area

In 1974, the countries around the Baltic Sea signed an agreement to protect the sea from pollution. This was the first time an agreement covered all pollution around a whole sea. It began working on May 3, 1980.

In 1992, a new agreement was signed by all the countries around the Baltic Sea and the European Community. This new agreement started working on January 17, 2000. It helps keep the Baltic Sea area clean, including the water, the sea bottom, and the land that drains into the sea. A group called the Helsinki Commission, or HELCOM, helps manage this agreement. The countries that agreed to follow it are Denmark, Estonia, the European Community, Finland, Germany, Latvia, Lithuania, Poland, Russia, and Sweden.

Coordination in the Baltic Sea region

The European Union helps countries around the Baltic Sea work together safely. After the Baltic States joined in 2004, the Baltic Sea became part of the EU. The EU started projects to share information and keep the waters safe.

The North Atlantic Treaty Organisation (NATO) also helps keep the area secure. After Finland joined in 2023 and Sweden in 2024, most countries around the Baltic Sea are now NATO members. NATO has started new projects to protect important underwater structures. One big yearly event is BALTOPS, a naval exercise held in the Baltic Sea.

The Nordic Defence Cooperation (NORDEFCO) is a group of Nordic countries — Denmark, Finland, Iceland, Norway, and Sweden — that work together on defense. It started in 2009 and aims to improve each country’s defense.

The Council of the Baltic Sea States is a group of ten European countries and the EU that meets regularly to discuss ways to make the region safer and more prosperous. It was created in 1992.