On 18 June 2025 Russia officially adopted a set of new maritime ‘baselines’ in the Baltic Sea, effectively dictating where foreign ships can and cannot sail in the vicinity of Russia’s coast. In particular, Decree 914establishes new straight baselines in the eastern Gulf of Finland that, among other things, precisely delineate the extent of Russia’s internal waters, which are off limits to foreign ships without the express authorization of the Russian government.
The question of exactly where Russia’s various maritime zones lie in the Baltic—and thus what rights Russian and foreign ships have in different parts of the sea—has become particularly salient since Russia’s full-scale invasion of Ukraine in 2022. After Finland and Sweden joined the alliance, the Baltic is now entirely surrounded by NATO member states, except for Russia’s small coastlines. There are strong suspicions in Europe and elsewhere that Russia is operating a ‘shadow fleet’ of oil tankers to evade international sanctions, including in the Gulf of Finland, some of which may also be involved in espionage and acts of sabotage. NATO’s military exercises and its new naval mission to protect critical infrastructure, Baltic Sentry, have only added to the militarization of the Baltic region—and with it, the risk of naval incidents with a potential for dangerous escalation.
In this Q&A, Dr Pierre Thévenin, a Researcher in SIPRI’s European Security Programme and for Expertise France, and an expert on maritime security and the law of the sea, explains what Russia’s new law says and its implications for peace and security in the Baltic.
Q: Briefly, what are baselines and why do they matter for coastal states?
PT: Baselines are the lines from which a state’s maritime zones are measured. Seaward of the baseline begins the state’s territorial sea. Any water on the landward side of a baseline is considered to be part of the state’s ‘internal waters’, where the state has the same sovereignty as it does on the land. This might include river deltas, lagoons and the sea between coastal islands, for example.
Under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), a state can claim an area of sea up to 12 nautical miles (about 22.2 kilometres) out from the baseline as territorial sea. It still has sovereignty there, but foreign ships can exercise the so-called right of innocent passage, which means they are free to sail through the territorial sea unimpeded, as long as they do nothing ‘prejudicial to the peace, good order or security of the coastal State’. This right of innocent passage even applies to warships.
In contrast, a foreign ship may not cross into a state’s internal waters without that state’s permission, and the state has a right to intercept and board any ship that does so. So it is very important to know where a state’s baselines lie.
Beyond the territorial sea, coastal states can claim a contiguous zone up to 24 nautical miles from the baselines, where they can board foreign ships that are heading for their territorial sea in order to prevent and punish customs, immigration and a few other violations—including breaching sanctions. Another zone, the exclusive economic zone, stretches up to 200 nautical miles from the baseline.
Q: What are straight baselines, and what does Decree 914 say about them?
PT: Baselines usually follow the low-water line of the coast. These are known as normal baselines. But where the coastline is more complex—for example, if it is deeply indented or fringed by islands—UNCLOS allows states to set a baseline by drawing straight lines between specific points on land—for example, on their islands or either side of the mouth of a deep bay. This can mean fairly large areas of sea become part of the state’s internal waters.
Decree 914 includes the coordinates of base points for drawing straight baselines across the Gulf of Finland, linking the Finnish–Russian border on the north side of the gulf to the Estonian–Russian border on the south side, at the Bay of Narva. The decree establishes Russian internal waters over almost the entire eastern end of the Gulf of Finland—about 150 km long. This includes the ports around Saint Petersburg (see figure 1).
Figure 1. Russia’s internal waters in the Gulf of Finland, according to Decree 914
Note: Straight baselines are estimated based on the base points published in Decree 914 of 18 June 2025. The locations of all base points, straight baselines and borders are approximate and for illustrative purposes only. The boundaries and names shown and the designations used in this map do not imply any endorsement or acceptance by SIPRI.
Map: SIPRI.
Q: Why did Russia want to establish new baselines?
PT: The question of exactly where Russia’s baselines lie in the Baltic had been left hanging since the end of the cold war. The last time Moscow had set baselines in the Baltic was in 1985, when the three Baltic states (Estonia, Latvia and Lithuania) were all part of the Soviet Union. The baselines in the Gulf of Finland thus went from the Finnish–Russian border down to the westernmost of the Russian islands in the gulf and then west along the northern coast of Estonia to the mouth of the gulf.
Since Estonia left the Soviet Union in 1991, it was never clear exactly where Russia’s baselines lay, particularly between the westernmost islands and the new Estonian–Russian border. This, of course, meant that a ship could unwittingly stray into a part of the Gulf of Finland that Russia considers to be its internal waters.
So, in many respects, Decree 914 is a bit of legal housekeeping that was long overdue, making it easier for everyone to know their rights and obligations in the Gulf of Finland and follow UNCLOS.
Q: How significantly do the new baselines change the situation in the Gulf of Finland?
PT: The answer is not very much. In practice, even if the 1985 baselines were clearly obsolete, everyone assumed that Russia considered the eastern end of the Gulf of Finland as its internal waters. The new baselines are very much in line with that assumption, and none of Russia’s neighbours has raised any objections to Decree 914.
It is important to note that baselines are not the same as maritime borders between states. By setting baselines, a state can define where its territorial waters and exclusive economic zones begin, but these zones automatically end at a maritime border. The Soviet Union and Finland agreedon their maritime border in 1965. In 2014 Estonia and Russia signed a treatyaimed at establishing their maritime border in the Bay of Narva and the Gulf of Finland. Although the treaty has not so far entered into force—Estonia is yet to complete the ratification process while Russia is yet to start it—the fact that the new straight baselines seem to use the same coordinates as the base points that were used on Russia’s coast during the negotiation of the maritime border in the Bay of Narva suggests Russia is not planning to challenge the previously drawn delimitation line.
One other important aspect of Decree 914 is that it says that normal baselines—following the low-water line of the coast—apply in the sea off the Russian exclave of Kaliningrad. This is a significant change from a draft law that briefly appeared on the government website in May 2024, which set straight baselines, including across the Strait of Baltiysk linking the Vistula Lagoon to the Baltic. This would have meant that Polish ships would have had to ask permission to sail through Russian internal waters to reach Polish ports in the southern end of the lagoon, which would arguably have contravened UNCLOS.
Q: What implications does the new law have for peace and security in the Baltic?
PT: It certainly makes everyone a bit safer, by reducing the risk of incidents that could lead to escalation. Given the current tensions between Russia and NATO, as well as the increase in NATO naval operations in the Baltic, the potential consequences of an Estonian, Finnish or other NATO member’s ship accidentally straying into Russian internal waters are much more serious than they were before 2022.
Now that Russia has finally published its baselines, ships know where they can and cannot freely move close to Russia’s Baltic coast.
Finally, there may be another diplomatic benefit for Russia, in that Decree 914 feeds into the image that Russia is trying to maintain of being a guardian of international law, and its broader narrative of being a fortress besieged by an aggressive West. This is the position Russia took in January 2023, when Estonia threatened to establish a contiguous zone in the Gulf of Finland. A few months later, Latvia’s president Edgars Rinkēvičs proposed denying Russia access to the Baltic if it could be proved that Russia was behind damage to the undersea Balticconnector gas pipeline connecting Estonia and Finland, although this would have violated Russia’s rights under UNCLOS.
ABOUT THE AUTHOR(S)
Dr Pierre Thévenin is a Researcher with SIPRI’s European Security Programme and an international technical expert for Expertise France.
On 18 June 2025 Russia officially adopted a set of new maritime ‘baselines’ in the Baltic Sea, effectively dictating where foreign ships can and cannot sail in the vicinity of Russia’s coast. In particular, Decree 914 establishes new straight baselines in the eastern Gulf of Finland that, among other things, precisely delineate the extent of Russia’s internal waters, which are off limits to foreign ships without the express authorization of the Russian government.
The question of exactly where Russia’s various maritime zones lie in the Baltic—and thus what rights Russian and foreign ships have in different parts of the sea—has become particularly salient since Russia’s full-scale invasion of Ukraine in 2022. After Finland and Sweden joined the alliance, the Baltic is now entirely surrounded by NATO member states, except for Russia’s small coastlines. There are strong suspicions in Europe and elsewhere that Russia is operating a ‘shadow fleet’ of oil tankers to evade international sanctions, including in the Gulf of Finland, some of which may also be involved in espionage and acts of sabotage. NATO’s military exercises and its new naval mission to protect critical infrastructure, Baltic Sentry, have only added to the militarization of the Baltic region—and with it, the risk of naval incidents with a potential for dangerous escalation.
In this Q&A, Dr Pierre Thévenin, a Researcher in SIPRI’s European Security Programme and for Expertise France, and an expert on maritime security and the law of the sea, explains what Russia’s new law says and its implications for peace and security in the Baltic.
Q: Briefly, what are baselines and why do they matter for coastal states?
PT: Baselines are the lines from which a state’s maritime zones are measured. Seaward of the baseline begins the state’s territorial sea. Any water on the landward side of a baseline is considered to be part of the state’s ‘internal waters’, where the state has the same sovereignty as it does on the land. This might include river deltas, lagoons and the sea between coastal islands, for example.
Under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), a state can claim an area of sea up to 12 nautical miles (about 22.2 kilometres) out from the baseline as territorial sea. It still has sovereignty there, but foreign ships can exercise the so-called right of innocent passage, which means they are free to sail through the territorial sea unimpeded, as long as they do nothing ‘prejudicial to the peace, good order or security of the coastal State’. This right of innocent passage even applies to warships.
In contrast, a foreign ship may not cross into a state’s internal waters without that state’s permission, and the state has a right to intercept and board any ship that does so. So it is very important to know where a state’s baselines lie.
Beyond the territorial sea, coastal states can claim a contiguous zone up to 24 nautical miles from the baselines, where they can board foreign ships that are heading for their territorial sea in order to prevent and punish customs, immigration and a few other violations—including breaching sanctions. Another zone, the exclusive economic zone, stretches up to 200 nautical miles from the baseline.
Q: What are straight baselines, and what does Decree 914 say about them?
PT: Baselines usually follow the low-water line of the coast. These are known as normal baselines. But where the coastline is more complex—for example, if it is deeply indented or fringed by islands—UNCLOS allows states to set a baseline by drawing straight lines between specific points on land—for example, on their islands or either side of the mouth of a deep bay. This can mean fairly large areas of sea become part of the state’s internal waters.
Decree 914 includes the coordinates of base points for drawing straight baselines across the Gulf of Finland, linking the Finnish–Russian border on the north side of the gulf to the Estonian–Russian border on the south side, at the Bay of Narva. The decree establishes Russian internal waters over almost the entire eastern end of the Gulf of Finland—about 150 km long. This includes the ports around Saint Petersburg (see figure 1).
Figure 1. Russia’s internal waters in the Gulf of Finland, according to Decree 914
Note: Straight baselines are estimated based on the base points published in Decree 914 of 18 June 2025. The locations of all base points, straight baselines and borders are approximate and for illustrative purposes only. The boundaries and names shown and the designations used in this map do not imply any endorsement or acceptance by SIPRI.
Map: SIPRI.
Q: Why did Russia want to establish new baselines?
PT: The question of exactly where Russia’s baselines lie in the Baltic had been left hanging since the end of the cold war. The last time Moscow had set baselines in the Baltic was in 1985, when the three Baltic states (Estonia, Latvia and Lithuania) were all part of the Soviet Union. The baselines in the Gulf of Finland thus went from the Finnish–Russian border down to the westernmost of the Russian islands in the gulf and then west along the northern coast of Estonia to the mouth of the gulf.
Since Estonia left the Soviet Union in 1991, it was never clear exactly where Russia’s baselines lay, particularly between the westernmost islands and the new Estonian–Russian border. This, of course, meant that a ship could unwittingly stray into a part of the Gulf of Finland that Russia considers to be its internal waters.
So, in many respects, Decree 914 is a bit of legal housekeeping that was long overdue, making it easier for everyone to know their rights and obligations in the Gulf of Finland and follow UNCLOS.
Q: How significantly do the new baselines change the situation in the Gulf of Finland?
PT: The answer is not very much. In practice, even if the 1985 baselines were clearly obsolete, everyone assumed that Russia considered the eastern end of the Gulf of Finland as its internal waters. The new baselines are very much in line with that assumption, and none of Russia’s neighbours has raised any objections to Decree 914.
It is important to note that baselines are not the same as maritime borders between states. By setting baselines, a state can define where its territorial waters and exclusive economic zones begin, but these zones automatically end at a maritime border. The Soviet Union and Finland agreed on their maritime border in 1965. In 2014 Estonia and Russia signed a treaty aimed at establishing their maritime border in the Bay of Narva and the Gulf of Finland. Although the treaty has not so far entered into force—Estonia is yet to complete the ratification process while Russia is yet to start it—the fact that the new straight baselines seem to use the same coordinates as the base points that were used on Russia’s coast during the negotiation of the maritime border in the Bay of Narva suggests Russia is not planning to challenge the previously drawn delimitation line.
One other important aspect of Decree 914 is that it says that normal baselines—following the low-water line of the coast—apply in the sea off the Russian exclave of Kaliningrad. This is a significant change from a draft law that briefly appeared on the government website in May 2024, which set straight baselines, including across the Strait of Baltiysk linking the Vistula Lagoon to the Baltic. This would have meant that Polish ships would have had to ask permission to sail through Russian internal waters to reach Polish ports in the southern end of the lagoon, which would arguably have contravened UNCLOS.
Q: What implications does the new law have for peace and security in the Baltic?
PT: It certainly makes everyone a bit safer, by reducing the risk of incidents that could lead to escalation. Given the current tensions between Russia and NATO, as well as the increase in NATO naval operations in the Baltic, the potential consequences of an Estonian, Finnish or other NATO member’s ship accidentally straying into Russian internal waters are much more serious than they were before 2022.
Now that Russia has finally published its baselines, ships know where they can and cannot freely move close to Russia’s Baltic coast.
Finally, there may be another diplomatic benefit for Russia, in that Decree 914 feeds into the image that Russia is trying to maintain of being a guardian of international law, and its broader narrative of being a fortress besieged by an aggressive West. This is the position Russia took in January 2023, when Estonia threatened to establish a contiguous zone in the Gulf of Finland. A few months later, Latvia’s president Edgars Rinkēvičs proposed denying Russia access to the Baltic if it could be proved that Russia was behind damage to the undersea Balticconnector gas pipeline connecting Estonia and Finland, although this would have violated Russia’s rights under UNCLOS.
ABOUT THE AUTHOR(S)