A strait is a narrow, natural stretch of water that connects two larger bodies of water and separates two areas of land. The Strait of Gibraltar, only about 14 km wide at its narrowest, links the Atlantic Ocean with the Mediterranean and separates Europe from Africa. Straits matter far more than their size suggests. Because ships must pass through them, a handful of straits, including Hormuz, Malacca, Bab-el-Mandeb, Gibraltar, Dover and the Bosphorus, act as chokepoints for a large share of world trade and energy supplies, and they are protected by special rules in international law.
Strait, Channel, Sound, Passage
Several words describe narrow waterways, and they overlap. A strait is the general geographic term. A channel is often a wider strait, as with the English Channel, which is about 240 km wide at its western end but narrows to about 33 km at the Strait of Dover. The word channel is also used for the deeper route that ships follow within any waterway. A sound can mean a strait, like the Øresund between Denmark and Sweden, or a wide inlet, like Puget Sound. Passage is used for broad routes between oceans, such as the Drake Passage between South America and Antarctica, about 800 km wide. The names often come from tradition rather than any strict rule. A strait is always natural. The Suez and Panama canals connect seas in the same way but were dug by people, so they are canals, not straits.
How Straits Form
Straits form in several ways. Some open as the Earth's plates move apart or slide past each other. The Strait of Gibraltar sits where the African and Eurasian plates meet. About 5.33 million years ago, after the Mediterranean had been cut off and largely dried up, the Atlantic broke through at Gibraltar and refilled the basin in what geologists call the Zanclean flood, possibly within a few years. Others were created by rising sea levels at the end of the last ice age, when meltwater flooded low land between areas of higher ground. The Bering Strait, the English Channel and the Torres Strait between Australia and New Guinea all formed this way.
While the ice ages locked up so much water that sea level was about 120 m lower than today, some of those straits were dry land. The land bridge of Beringia joined Asia and North America across what is now the Bering Strait, and it was probably the route by which the first people reached the Americas. Britain was joined to the continent by a low plain, now called Doggerland, until it was flooded around 8,000 years ago.
The Chokepoints of World Trade
The Strait of Hormuz, between Iran and the Musandam peninsula of Oman, is about 33 km wide at its narrowest, with shipping lanes only a few kilometres wide in each direction. Around a fifth of the oil consumed in the world passes through it each day, together with much of the world's liquefied natural gas from Qatar, which is why any threat to close it moves global oil prices. Our guide to the Strait of Hormuz explains the shipping lanes.
The Strait of Malacca, between the Malay Peninsula and the Indonesian island of Sumatra, is the main route between the Indian Ocean and the Pacific. Tens of thousands of ships pass through it each year, carrying a large share of the trade between Europe, the Middle East and East Asia, including most of the oil that China, Japan and South Korea import. At its southern end, in the Singapore Strait, the navigable channel narrows to less than 3 km. Chinese leaders have spoken of a "Malacca dilemma", the risk of relying on a passage that could be blocked. More is in our guide to the Strait of Malacca.
The Bab-el-Mandeb, whose Arabic name means "gate of grief", links the Red Sea with the Gulf of Aden between Yemen and Djibouti, and so controls the southern approach to the Suez Canal. Attacks on shipping by Yemen's Houthi movement from late 2023 led many shipping lines to avoid the Red Sea and sail around the Cape of Good Hope instead, adding days and cost to journeys between Asia and Europe.
Gibraltar, Dover and the Turkish Straits
Europe's own straits have shaped its history. The Strait of Gibraltar controls the only natural entrance to the Mediterranean from the ocean. Its currents are unusual. Less salty Atlantic water flows in at the surface, while denser, saltier Mediterranean water flows out along the bottom, a two-way exchange that German submarines in the Second World War used to drift through quietly with their engines off. The strait is described in our guide to the Strait of Gibraltar.
The Strait of Dover, about 33 km wide, is one of the busiest shipping lanes in the world, and ships follow a traffic separation scheme like lanes on a motorway. It is the narrowest point of the English Channel. The Channel Tunnel, opened in 1994, runs beneath it, and swimmers have crossed it since Matthew Webb first did so in 1875.
The Bosphorus, which divides Istanbul between Europe and Asia, is only about 700 m wide at its narrowest. Together with the Sea of Marmara and the Dardanelles, it forms the Turkish Straits, the only sea link between the Black Sea and the Mediterranean. Their use is governed by the Montreux Convention of 1936, which guarantees merchant ships free passage in peacetime and limits the warships that non-Black Sea countries can send through.
Straits in War
Control of straits has decided battles and campaigns for thousands of years. In 480 BCE the Greek fleet defeated a much larger Persian navy in the narrow strait between the island of Salamis and the Greek mainland, where the Persians could not use their numbers. In 1915 British, French and Commonwealth forces tried to force the Dardanelles and open a sea route to Russia. The naval attack failed, and the land campaign at Gallipoli ended in withdrawal after months of fighting and hundreds of thousands of casualties on both sides. In May 1967 Egypt closed the Straits of Tiran, at the mouth of the Gulf of Aqaba, to Israeli shipping, one of the immediate causes of the Six-Day War that June. During the Iran–Iraq War of the 1980s, attacks on tankers in and around the Strait of Hormuz led foreign navies to escort merchant ships through the Gulf.
What International Law Says
Because straits are so important, they have special status in international law. Countries may claim a territorial sea up to 12 nautical miles, about 22 km, from their coasts, so any strait narrower than 24 nautical miles can lie entirely within one or two countries' waters. The UN Convention on the Law of the Sea of 1982 created a right of transit passage through straits used for international navigation. Ships and aircraft of every country may pass through continuously and quickly, and the coastal states may not suspend that right, even though the water is part of their territory. The principle goes back to the Corfu Channel case of 1949, when the International Court of Justice ruled that Albania was responsible for mines in a strait that damaged British warships.
Bridges, Tunnels and Wildlife
Many straits have now been crossed by engineering. Japan's Seikan Tunnel, under the Tsugaru Strait between Honshu and Hokkaido, is about 54 km long and opened in 1988. The Akashi Kaikyō Bridge across the Akashi Strait near Kobe, opened in 1998, held the record for the longest main span of any suspension bridge for more than two decades. In 2022 that record passed to the 1915 Çanakkale Bridge across the Dardanelles, whose central span is 2,023 m long. The Bosphorus has been bridged since 1973, and the Marmaray rail tunnel beneath it opened in 2013.
Straits are also funnels for wildlife. Storks, eagles and other large soaring birds avoid long sea crossings because they rely on rising warm air, which forms over land. So hundreds of thousands of them gather to cross at Gibraltar and the Bosphorus on their migrations between Europe and Africa. Whales and dolphins pass through straits too. Since 2020, orcas near the Strait of Gibraltar have been ramming and damaging the rudders of sailing boats, a behaviour scientists are still trying to explain.
Other Straits Worth Knowing
Many other straits have their own stories. Ferdinand Magellan's expedition found the Strait of Magellan through southern South America in 1520, a sheltered route between the Atlantic and the Pacific. The Bering Strait, about 82 km wide, separates Russia and the United States, with the two Diomede Islands in the middle and the International Date Line running between them. The Taiwan Strait, about 130 to 180 km wide, separates Taiwan from mainland China. The Strait of Messina, only about 3 km wide between Sicily and mainland Italy, was feared in ancient times as the home of the monsters Scylla and Charybdis because of its whirlpools and currents. The Øresund between Denmark and Sweden has been crossed by a combined bridge and tunnel since 2000.