Home › Water › Straits & Canals
The Danish Straits
The three channels through the Danish islands that are the Baltic Sea's only sea routes to the North Sea and the Atlantic
The Baltic Sea is almost enclosed, and every ship sailing from St. Petersburg, Gdańsk or Helsinki to the open ocean has to thread one of three channels through the Danish islands: the Øresund, the Great Belt or the Little Belt. Together they are known as the Danish Straits. For more than four centuries Denmark charged a toll, the Sound Dues, on ships passing Elsinore, until a treaty in 1857 opened the waters to all. Today the straits carry container ships, ferries, naval vessels and a heavy flow of oil, about 4.5 million barrels a day in the first half of 2025 according to S&P Global estimates, much of it Russian crude and refined products.
The straits link the Baltic with the Kattegat, which opens north through the Skagerrak into the North Sea. The Øresund, shared by Denmark and Sweden, is about 4 kilometers wide at its narrowest between Helsingør and Helsingborg, but shallow sills south of Copenhagen limit ships to drafts of about 8 meters. The Great Belt, between the islands of Zealand and Funen, is the deep-water route: its main channel, Route T, takes ships drawing up to about 15 meters and is the path for large tankers. The Little Belt, between Funen and Jutland, is narrow and winding and carries mostly smaller vessels. Fixed links cross all three, including the Great Belt Bridge of 1998 and the Øresund Bridge of 2000, while a road and rail tunnel under the Fehmarn Belt to Germany is under construction.
Denmark collected the Sound Dues from the 1420s, and the revenue helped pay for Kronborg Castle at Elsinore, the setting of Shakespeare's Hamlet. Pressure from the United States and other trading nations led to the Copenhagen Convention of 1857, under which Denmark abolished the dues in return for a one-time compensation and the straits became open to commercial shipping. The Great Belt and Little Belt lie within Danish territorial waters, while the Øresund is shared with Sweden, and the passage is still governed by that long-standing treaty. Since 2022 the straits have drawn attention as the exit route for aging tankers that Western governments describe as Russia's shadow fleet. In October 2025 Denmark announced tighter environmental inspections at the Skagen anchorage. The Fehmarn Belt tunnel, once due in 2029, is now expected around 2031.