47 Fun Facts About Baltic Sea

Which sea fortress did Sweden build off Helsinki from 1748?

Suomenlinna was built by Sweden to guard against Russia, yet in 1808 its commander surrendered it to Russian forces, for reasons that remain unclear.

The Baltic is often called the world's largest basin of what kind of water?

Brackish water fills the Baltic because rivers draining an area over four times its size pour in fresh water, while ocean salt can enter only through the narrow Danish straits.

Which sea does the Baltic drain into through the Danish Straits?

The Kattegat is shallow, and its reefs and uneven seabed make it a tricky passage for ships.

Which artificial waterway, opened in 1895 through Schleswig-Holstein, links the Baltic to the North Sea?

The Kiel Canal was sought by merchants and by the German navy, which wanted to link its Baltic and North Sea bases without sailing around Denmark.

What is the northern arm of the Baltic, lying between Sweden and Finland, called?

The Gulf of Bothnia's northern shores rise about 1 cm a year, as the land rebounds from the weight of the ice-age ice sheet.

Which arm of the Baltic connects the sea to Saint Petersburg?

The Gulf of Finland's storm surges long flooded Saint Petersburg, so a flood barrier abandoned in the 1990s was finally completed in 2011.

At which research site on the Baltic island of Usedom did Wernher von Braun's team develop the V-2 rocket?

Peenemünde developed the V-2, but the rockets were mass-produced largely by concentration camp prisoners, at least 10,000 of whom died making them.

Which Roman historian, writing about the Germanic tribes, called the Baltic the 'Suebic Sea'?

Tacitus may never have set foot in Germania himself, so his account of its tribes may rest largely on second-hand reports.

Which 18th-century Swedish scientist had marks cut into coastal rocks to measure the Baltic's apparent fall?

Anders Celsius's marks tracked a retreating shoreline, and the cause is now known to be the land itself rising, not the sea falling.

In German, Swedish, Danish and most other Germanic languages the Baltic is called the equivalent of what?

German Ostsee and Swedish Östersjön both mean East Sea, yet Estonian flips the idea: its name, Läänemeri, means West Sea.

Which film spaceship did some liken to the sonar 'anomaly' Swedish treasure hunters found on the Baltic seabed in 2011?

The Millennium Falcon comparison did not hold up: a geologist who examined the divers' samples found only natural rock.

Which gem-like material do beachcombers famously gather along the Baltic's southern shores after storms?

Amber is fossilised tree resin: waves tear pieces from the seabed and storms cast them ashore, where people still collect them by hand.

Which federation of merchant towns, grown from Lübeck, dominated Baltic trade from the 13th to 16th centuries?

The Hanseatic League grew from Lübeck's 1241 pact with Hamburg into a network of some 200 towns; its Kontors in London, Bruges, Bergen and Novgorod enjoyed their own legal privileges.

Which type of medieval merchant ship was pictured on the seals of Baltic trading towns such as Lübeck?

The cog was known mainly from such seals until 1962, when dredging in Bremen's river Weser uncovered a well-preserved wreck from about 1380.

Which Latin phrase named the goal of Poland, Denmark and Sweden's 16th–17th-century Baltic wars?

Dominium maris baltici means lordship over the Baltic; Sweden came closest to it, until Russia defeated Sweden in a war that ended in 1721.

At which castle near Helsingør did Denmark collect its Sound Dues from ships passing through the Øresund?

Kronborg's guns enforced the Sound Dues: a ship that refused to pay could be fired on, until Denmark abolished the toll in 1857.

Which Russian ruler founded Saint Petersburg at the mouth of the Neva to secure a Baltic outlet?

Peter the Great had earlier spent 18 months touring Western Europe incognito, a journey known as the Grand Embassy.

Where in the Baltic did an Anglo-French force destroy Russia's Bomarsund fortress in 1854?

Åland's Bomarsund fortress was captured and destroyed in 1854, and the peace that ended the war left the islands demilitarised.

Which German refugee ship, torpedoed in January 1945, is thought to be history's deadliest single-ship sinking?

The Wilhelm Gustloff sank within an hour, and many who survived the torpedoes and the chaos on board froze to death in the icy Baltic.

What ran aground near Sweden's Karlskrona naval base in October 1981, setting off a Cold War standoff?

A Soviet submarine, called U137 by the Swedes, had run aground, and Swedish radiation tests suggested it was carrying nuclear weapons.

The ferry MS Estonia sank in September 1994 while sailing between which two cities?

The Estonia had left Tallinn for Stockholm when her bow visor tore away and pulled open the car-deck ramp, letting in the water that sank her; 852 people died.

Why have wooden wrecks such as the Vasa survived so well on the Baltic seabed?

Shipworms are rare there because they need saltier water than most of the Baltic offers, so wooden wrecks last far longer there than in the oceans.

Why did the Swedish warship Vasa sink minutes into her maiden voyage in 1628?

She was top-heavy and unstable, so a wind barely stronger than a breeze heeled her over, and about 30 people died when she sank.

In which Swedish town was the 1397 union of Denmark, Norway and Sweden under one monarch agreed?

Kalmar gave its name to the union, but Sweden broke away for good in 1523, when it elected its own king.

Which Baltic fish is fermented to make Sweden's notoriously pungent surströmming?

Herring keeps fermenting inside surströmming's tins, which is why airlines such as British Airways banned the cans as potentially explosive.

Which Baltic seal gives birth only on the winter sea ice, hiding its pup in a snow lair?

The ringed seal raises its pup in snow lairs on the ice, so winters with too little ice mean weaker pups and more of them dying.

What are the occasional pulses of salty, oxygen-rich North Sea water that flush the deep basins called?

Major Baltic inflows are the deep basins' only real supply of fresh oxygen: the dense, salty North Sea water sinks along the seabed and pushes out the stale water.

What mainly fuels the algal blooms that starve the Baltic seafloor of oxygen?

Nitrogen and phosphorus feed the blooms, and as the dead algae sink and rot, their decay uses up the oxygen near the seabed.

Which is Sweden's largest island, home to the walled medieval town of Visby?

Gotland's Visby grew rich as a Baltic trading hub, but in 1361 Denmark's King Valdemar IV invaded the island and held the town to ransom.

Which Danish Baltic island is famous for its round churches and the fortress ruin of Hammershus?

Bornholm lies east of the rest of Denmark, so travellers from Copenhagen often cross into Sweden and take a ferry from Ystad.

Which World Heritage peninsula is shared by Lithuania and Russia's Kaliningrad region?

The Curonian Spit lost most of its forests, and drifting sand overran whole villages until large-scale replanting began in the 19th century.

The Øresund Bridge connects Malmö with which Danish island?

The link lands on Amager, the island holding Copenhagen Airport: the bridge from Malmö ends on an artificial islet mid-strait, and a 4 km immersed tunnel carries road and rail onward so flights and shipping stay clear.

Which artificial island in the middle of the Øresund joins the Øresund Bridge to its tunnel?

Peberholm was built for the railway and motorway, not for wildlife, yet left to itself it has been colonised by birds and hundreds of plant species.

After Finland and Sweden joined the Western alliance in 2023 and 2024, commentators nicknamed the Baltic what?

With Finland and Sweden in NATO, every Baltic shore except Russia's, around St Petersburg and the Kaliningrad exclave, belongs to the alliance, hence 'a NATO lake'.

Which gas pipelines on the Baltic seabed were destroyed by underwater explosions in September 2022?

Seismic stations recorded large underwater blasts just before Nord Stream 1 and 2 began leaking, yet Sweden and Denmark closed their inquiries without naming a culprit.

Which of these major rivers flows into the Baltic Sea?

The Vistula is the longest river draining into the Baltic, yet the Neva, flowing out of Lake Ladoga, pours in more than twice as much water.

Which cetacean has a critically endangered population living in the central Baltic Sea?

The harbour porpoise often drowns as bycatch in fishing nets, a key threat to the Baltic population.

In 1904, gunners of Russia's Baltic Fleet fired on British fishing trawlers, mistaking them for whose torpedo boats?

Japanese torpedo boats were what the fleet feared, but most members of the international commission that investigated found none among the trawlers or anywhere near.

What was the German naval operation that carried troops and civilians west across the Baltic from January to May 1945?

Operation Hannibal rescued Germans trapped in East Prussia after the Red Army's advance cut the province off from the rest of Germany by land.

The Baltic's eastern shore was among the last of Europe to be Christianised, during which campaigns?

The Northern Crusades left the Teutonic Order ruling a crusader state on the Baltic shore that even swallowed Danzig in 1308.

Which interwar territory, awarded at Versailles, held the Baltic port of Gdynia?

The Polish Corridor gave reborn Poland its route to the Baltic, but it cut East Prussia off from the rest of Germany.

Which German island, the country's largest, lies in the Baltic off the Pomeranian coast?

Rügen's white chalk cliffs inspired the German Romantic painter Caspar David Friedrich's famous canvas Chalk Cliffs on Rügen.

Which pirate band made Visby its base in the 1390s, until the Teutonic Order drove it out in 1398?

The Victual Brothers began as blockade-runners hired by the Dukes of Mecklenburg in their war with Denmark's Queen Margaret, then turned to open piracy.

At which naval base did Baltic Fleet sailors revolt against Lenin's Bolsheviks in 1921?

Kronstadt's revolt was crushed in March 1921, when Red Army troops stormed the island fortress across the frozen sea before the ice could melt.

Which three Danish straits link the Baltic Sea to the North Sea?

The Øresund, Great Belt and Little Belt were once all Danish waters, but since Denmark lost Scania to Sweden in 1658 it has shared the Øresund.

The Gulf of Riga lies between the Latvian capital and which Estonian island?

Saaremaa, Estonia's largest island, closes the Gulf of Riga on the north-west; the gulf opens to the Baltic through the Irbe Strait between Saaremaa and Latvia's Courland coast, with Riga at its southern head.

Which Swedish king shipped his army across the Baltic to Pomerania in 1630 to enter the Thirty Years' War?

Gustavus Adolphus won his greatest victory at Breitenfeld in 1631, but a year later he was killed on the battlefield at Lützen.