50 Fun Facts About Baltic Sea

How many countries have a coastline on the Baltic Sea?

Nine countries touch the Baltic: Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden; Belarus, Norway and others lie only in its drainage basin.

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

The Baltic is brackish: rivers draining an area four times the sea's pour in fresh water, while salt water can enter only over the shallow Danish sills, the Drogden just 7 m deep, so it stays fresher than the ocean.

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

The Danish straits open into the Kattegat, the shallow sea between Jutland and Sweden; only beyond it, through the Skagerrak, do Baltic waters reach the North Sea.

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

The Kiel Canal, opened in 1895 as the Kaiser-Wilhelm-Kanal, runs 98 km from Brunsbüttel on the Elbe to Kiel-Holtenau, sparing ships a detour of roughly 460 km around Jutland.

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

The Gulf of Bothnia runs about 725 km north from the Archipelago Sea to Tornio, with Sweden on its west shore and Finland on its east; its northern basin, the Bothnian Bay, freezes over every winter.

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

Saint Petersburg stands at the eastern end of the Gulf of Finland, where the Neva enters the sea; the city was founded there in 1703 on ground just taken from Sweden.

What is the maximum depth of the Baltic Sea, at the Landsort Deep on the Swedish side?

The Landsort Deep, southwest of Stockholm, reaches about 459 m, the Baltic's deepest point; the sea as a whole averages only around 55 m, which is why river runoff freshens it so easily.

Which Roman historian described the 'Suebic Sea' (Mare Suebicum), an early name for the Baltic, in AD 98?

Tacitus described the Mare Suebicum in his Germania of AD 98, naming it after the Suebi; Ptolemy later preferred 'Sarmatian Ocean'.

Which 11th-century German chronicler first called it the 'Baltic Sea', likening it to a belt?

Adam of Bremen, writing around 1075, was the first to call it Mare Balticum, saying the sea stretched like a belt (Latin balteus) through the north; the name only became standard after 1600.

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

German Ostsee, Swedish Östersjön and Danish Østersøen all mean East Sea; Estonian reverses it as Läänemeri, 'West Sea', while Finnish Itämeri keeps 'East Sea', a calque from Swedish.

What did the Vikings call the Baltic, a name meaning 'Eastern Sea' that appears in the Heimskringla?

Austmarr, 'Eastern Sea', is the name used for the Baltic in Snorri's Heimskringla, in a verse of the Ynglinga saga; Norse traders crossed it eastward to Gardariki, the lands of the Rus.

Which fossilised resin has been harvested on the Baltic's south shores since the 12th century?

Amber, the fossilised resin of ancient conifers, is mined and beachcombed along the southern Baltic; the Sambia peninsula in Russia's Kaliningrad region holds around 90 percent of the world's known deposits.

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.

What was the emblematic ship type of the Hansa merchants, depicted on its seals and coats of arms?

The cog, a single-masted, clinker-built trader with a flat bottom and high sides, appears on the seals of Lübeck, Stralsund and other Hansa towns; by the late Middle Ages it gave way to the hulk.

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

Dominium maris baltici, 'lordship of the Baltic Sea', was the prize Denmark, Sweden and Poland fought over from the 1560s Northern Seven Years' War to the 1720s; Sweden held it longest, though Dutch ships carried most of the trade.

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

Kronborg, rebuilt from the older Krogen fortress in the 1570s, guards the narrowest point of the Øresund at Helsingør, where Denmark levied the Sound Dues from 1429 until 1857; it is also Hamlet's Elsinore.

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

Peter the Great founded Saint Petersburg in May 1703 on the Neva delta, on ground captured from Sweden, and moved his capital there in 1712 to anchor Russia on the Baltic.

In the Crimean War, Russia's Bomarsund fortress was destroyed in which Baltic archipelago?

Bomarsund stood on Åland; an Anglo-French force captured and demolished it in August 1854, and in Finland the Baltic theatre is known as the Åland War. The fleet shelled Sveaborg off Helsinki in 1855.

Which German ship, sunk in January 1945, caused history's deadliest maritime disaster?

The Wilhelm Gustloff, packed with refugees from East Prussia, was torpedoed by the Soviet submarine S-13 on 30 January 1945; about 9,000 people died in the freezing Baltic, more than on any other single ship.

Which Soviet submarine commander sank the German evacuation ship Gustloff on 30 January 1945?

Alexander Marinesko, captain of the submarine S-13, trailed the Gustloff for about two hours, then swung round to attack from the landward side, where no escort expected a submarine; three torpedoes struck.

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

The Estonia was sailing between Tallinn and Stockholm on the night of 27–28 September 1994 when the bow visor's locks failed in heavy seas; water flooded the car deck and she sank within about an hour, killing 852 people.

Why do old wooden wrecks such as the Vasa survive so well on the Baltic seabed?

The cold brackish water keeps out the shipworm Teredo navalis, which bores through wooden hulls in saltier seas; that is why the Vasa, on the bottom off Stockholm for 333 years, was raised largely intact in 1961.

How far did the Swedish warship Vasa get into her maiden voyage in 1628 before she sank?

Vasa had covered only about 1,300 metres of her maiden voyage on 10 August 1628 when a gust heeled her over, water poured in through the open gunports and she sank in Stockholm harbour; the inquiry punished nobody.

Since 1720, how many times has the Baltic Sea frozen over entirely, most recently in early 1987?

The Baltic has frozen over completely 20 times since 1720, the last in the severe winter of early 1987; in a typical winter only the Gulfs of Bothnia, Finland and Riga ice over, and even 2010–11 fell short.

Roughly what fraction of the Baltic Sea's surface is ice-covered at an average winter's peak?

About 45% of the Baltic's surface freezes in an average winter, essentially the Gulf of Bothnia, the Gulf of Finland and the Archipelago Sea, with ice peaking in February or March; the Bothnian Bay freezes first and thaws last.

Which two seal species depend on the sea's winter ice, one of them breeding only on it?

The Baltic's grey and ringed seals both pup on the winter ice, but the ringed seal does so exclusively, rearing its pups in snow lairs on the ice, while the grey seal can also breed on skerries ashore.

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

Oceanographers call them Major Baltic Inflows: strong westerly storms push dense, oxygen-rich North Sea water through the Danish straits into the deep basins. Big ones came in 1993, 2003 and 2014, each reviving the anoxic central deeps.

Approximately what share of the Baltic seafloor is a variable 'dead zone' with almost no oxygen?

Roughly a quarter of the seafloor, about 100,000 km², is a shifting dead zone: dense salty water lies trapped below the halocline, bacteria there release hydrogen sulphide, and fertiliser runoff feeding summer algal blooms makes it worse.

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

Gotland, at roughly 3,000 km² Sweden's largest island, has Visby as its capital; the medieval town wall and warehouses earned it UNESCO World Heritage status in 1995, and it hosts Almedalen Week each summer.

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

Bornholm, far east of the rest of Denmark, has four medieval round churches and Hammershus, one of Northern Europe's largest castle ruins; Soviet troops bombed and occupied it in May 1945 and stayed until April 1946.

Which curved sand-dune peninsula, a World Heritage Site, is shared by Lithuania and Russia's Kaliningrad region?

The Curonian Spit, a 98 km ribbon of dunes dividing the Curonian Lagoon from the Baltic, was inscribed by UNESCO in 2000; Thomas Mann summered at Nida on the Lithuanian half from 1930 to 1932.

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.

What is the name of the artificial island in the middle of the Øresund where the bridge meets the tunnel?

Peberholm, 'Pepper Islet', was built from dredged seabed in the 1990s and named as a pun on its natural neighbour Saltholm, 'Salt Islet'; it is a nature reserve where the bridge's road and rail dip into the Drogden Tunnel.

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

With Finland (April 2023) and Sweden (March 2024) in NATO, every Baltic shore except Russia's, around St Petersburg and the Kaliningrad exclave, belongs to the alliance, hence the nickname 'a NATO lake'.

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

Nord Stream 1 and 2, the gas links from Russia to Germany, were ruptured by explosions near Bornholm on 26 September 2022; a year later the Balticconnector pipeline was damaged by a ship's dragging anchor, and NATO launched Baltic Sentry.

Which of these major rivers flows into the Baltic Sea?

The Vistula, Poland's longest river at about 1,047 km, enters the Baltic at Gdańsk; the Oder, Neman, Daugava and Neva also drain into it, while the Elbe and Rhine reach the North Sea and the Dnieper the Black Sea.

Roughly how many people live in the Baltic Sea's drainage basin?

About 85 million people live in the Baltic's drainage basin, which at some 1.7 million km² is more than four times the size of the sea; Poland, almost all of whose territory drains into it, holds the largest share.

What do palaeontologists call the great river whose plain occupied the Baltic's site before the ice ages?

Geologists call it the Eridanos, after the mythical amber river; it drained much of northern Europe into a delta in the present Baltic basin until the Pleistocene ice sheets obliterated it, leaving later stages like the Baltic Ice Lake.

After the Ice Age lake stage, the Baltic basin passed through a freshwater phase named for which mollusc?

The Ancylus Lake lasted from roughly 10,700 to 9,800 years ago, between the Yoldia Sea and the saltier Littorina Sea.

How salty is the open surface water of the Baltic proper, compared with the ocean average of 3.5%?

Surface salinity in the Baltic proper is only 0.3 to 0.9%, near-fresh beside the ocean's 3.5%: the saltiest water, 0.7–0.9%, lies in the south-west near the Danish islands, the freshest at the top of the Bothnian Bay.

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

The Northern Crusades, from the 1147 Wendish Crusade to the 13th-century Livonian campaigns, brought Swedes into Finland and Danes and Germans into Estonia and Latvia; Lithuania, the last pagan state in Europe, converted only in 1387.

After WWII, what did several nations dump into the Baltic that trawlers have since hauled up?

Around 40,000 tonnes of chemical weapons, mostly German mustard-gas and arsenic munitions, were dumped in the Bornholm and Gotland deeps after 1945, largely by the Soviet Union; corroded shells regularly turn up in trawl nets.

Which region of Poland gained a Baltic port at Gdynia after 1920, rivalling the Free City of Danzig?

The Polish Corridor, the strip of Pomerelia awarded to Poland at Versailles, gave the reborn state its only sea access; Gdynia, a fishing village in 1920, outstripped Danzig's cargo tonnage by the mid-1930s.

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

Rügen, at about 926 km² Germany's largest island, lies off the Pomeranian coast and is linked to Stralsund by bridge; its chalk cliffs in Jasmund National Park were painted by Caspar David Friedrich.

Which pirate brotherhood held Sweden's largest island during the era of Baltic piracy?

The Victual Brothers, privateers first hired in 1392 to provision besieged Stockholm, turned to open piracy and held the island and Visby from the mid-1390s until the Teutonic Order drove them out in 1398.

How long is the Baltic Sea from end to end, roughly?

The Baltic runs about 1,600 km from the Danish straits to the head of the Bothnian Bay, averages only 193 km in width and about 55 m in depth, and has some 8,000 km of coastline.

Which three Danish straits connect the Baltic with the Kattegat?

The Øresund, Great Belt and Little Belt thread between Sweden, Zealand, Funen and Jutland; the Great Belt, spanned since 1998 by an 18 km bridge-and-tunnel link, carries most of the deep-draught shipping.

Which 1658 treaty transferred Scania, Halland and Blekinge from Denmark to Sweden?

The Treaty of Roskilde, signed in February 1658 after Charles X Gustav marched his army across the frozen Belts, made Denmark cede Scania, Halland and Blekinge, fixing the Swedish shore of 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.

What is the approximate surface area of the Baltic Sea?

The Baltic covers about 350,000 sq km, close to the area of Germany, yet holds only around 20,000 cubic km of water because much of it is shallow, averaging about 55 m deep.