Maritime Zones

The United Nations Convention on the Law of the Sea (UNCLOS) divides the world’s oceans into a series of legally distinct maritime zones, which each confer different rights and obligations on the coastal states they belong to and other users of the sea.

These zones attempt to balance two competing principles: mare clausum (directly translated as “the closed sea”, this refers to the extension of coastal state jurisdiction) and mare liberum (directly translated as “the free sea”, this refers to the preservation of the oceans as a shared domain for navigation, commerce, and security). These principles – and conflicting views how they should be interpreted and applied – have been a major and persistent source of geopolitical tensions.  

In this article we will cover each of these maritime zones, beginning with internal waters and extending seaward out to the high seas, outlining their legal status, scope, and key areas of controversy.

Baseline: A baseline is the legal line that separates a state’s internal waters from its territorial sea. It can be drawn in several ways, each affecting the extent and boundaries of the maritime zones measured from it in different ways:

Coastal State: A sovereign nation that has a coastline bordering an ocean, sea, or large body of water. It is used in this article to denote a state with some level of sovereignty over a particular maritime zone.

Flag State: The state where a vessel is registered and licensed, giving the ship its legal nationality and the right to fly that country’s flag.

Internal waters include all waters on the landward side of a coastal state’s baseline, such as ports, harbours, rivers, estuaries, and bays.  

Coastal states have equivalent sovereignty over their internal waters as they do over their land. As such, foreign warships and governments typically require explicit permission to enter them.

For Analysts: The ability to grant or deny access to ports or harbours gives coastal states leverage in trade and other diplomatic negotiations. Admission can be interpreted as a signal of alignment, while denial can be seen as hostile or coercive, and can escalate into diplomatic disputes.

Other areas of contention include the drawing of straight baselines, which can convert previously open waters into internal waters, and claims based on historic bays or historic titles (particularly where they restrict navigation routes).

Internment of Polish Submarines: During the Second World War, neutral states controlled belligerent warships’ access to their ports. In September 1939, Sweden admitted three damaged Polish submarines - ORP Sęp, Ryś and Żbik - but disarmed the vessels and interned their crews, preventing more than 170 sailors from returning to combat.

These measures followed the 1907 Hague Convention, which allowed neutral governments to regulate such visits and generally limited belligerent warships to 24 hours in port. Read more.

Territorial seas extend 12 nautical miles seaward from a coastal state’s baseline unless constrained by overlapping claims from a neighbouring coastal state, in which case they typically extend to the median line between their coastlines.

A coastal state has full sovereignty over the water column, seabed, subsoil, and airspace within and above its territorial seas. However, this is qualified by the right of innocent passage which allows foreign vessels to transit the zone without prior permission, providing certain conditions are met.

For Analysts: Some coastal states argue that transit by foreign warships does not qualify as “innocent passage” and require prior notification or authorisation, allowing them to restrict foreign military activity near their shores.

In response, naval powers may conduct freedom of navigation operations (FONOPs) in an effort to protect their rights to navigate through the waters in question, which can lead to naval encounters and diplomatic protests.

The Corfu Channel Incident: In 1946, British warships passing through Albanian waters struck naval mines, killing 44 sailors and damaging two vessels. Albania claimed the passage violated its sovereignty, while Britain argued that its warships were legally-permitted to pass through straits used for international navigation.

The International Court of Justice ruled that the passage was lawful and that Albania was responsible for failing to warn ships about the minefield. The ruling helped establish the principles of innocent passage and international straits which were later incorporated in UNCLOS. Read more.

A contiguous zone is a maritime area extending from the seaward edge of a coastal state’s territorial sea to 24 nautical miles from its baseline.

Within this zone, the coastal state may take necessary measures to prevent and punish breaches of its customs, fiscal, immigration, and sanitary laws committed within its territory or territorial seas.

For Analysts: Contiguous zones function as a buffer between a coastal state’s territorial waters and the high seas, allowing states to extend authority seaward without formally expanding territorial claims - making them important tools of maritime and foreign policy.

However, when states use contiguous zones to justify broader security or military controls not explicitly authorised under UNCLOS – for instance attempting to exert authority over foreign vessels as though they were operating within their territorial waters – it can lead to disputes.

The Hovering Acts: Smuggling around British ports led authorities to extend customs enforcement beyond territorial waters. The Hovering Acts of 1718 and 1784 allowed officers to intercept vessels “hovering” or lingering offshore with goods associated with smuggling before they reached the coast, without claiming sovereignty over the surrounding sea.

Similar practices spread internationally and contributed to formal recognition of the contiguous zone in the 1958 Geneva Convention and later UNCLOS. Read more.

EEZs extend up to 200 nautical miles from a coastal state’s baseline. Within them, coastal states have sovereign rights for the purpose of exploring, exploiting, conserving, and managing natural resources in the water column, seabed, and subsoil. They are also permitted to enforce conservation measures, board vessels engaged in unlawful fishing, and regulate maritime scientific research.

Other states retain freedoms of navigation and overflight, as well as the laying of submarine cables and pipelines.

For Analysts: EEZs encompass the majority of commercially viable offshore resources. Therefore, taking or retaining control over an EEZ can have a major impact on a state’s food and energy security and industrial strategy – meaning strategic competition over who owns them can be fierce.

Overlapping boundary claims – usually resulting from differing interpretations of coastal baselines – mean a single area of ocean can be claimed as an EEZ by multiple states. States looking to protect or establish these claims often do so by attempting to normalise military activity and presence, which inevitably leads to naval encounters and major diplomatic disputes.

Cod Wars: Between 1958 and 1976, Iceland extended its fishing limit from 12 to 50 and eventually 200 nautical miles. Icelandic patrol vessels enforced these claims by pursuing British trawlers and cutting their nets, leading to repeated confrontations with the Royal Navy.

Although the International Court of Justice ruled on the 50-mile dispute in 1974, Iceland rejected its authority and continued expanding its fishing zone. Britain recognised the 200-mile limit in 1976, shortly before it adopted one of its own. The 200-mile EEZ was later included in UNCLOS. Read more.

A continental shelf is defined as the seabed and subsoil extending beyond a coastal state’s land territory to the outer edge of its continental margin. Under UNCLOS, it is legally distinct from the water column above it and exists independently of whether a state declares it. All states are entitled to a continental shelf extending 200 nautical miles from their baseline. If the natural continental margin extends further, states can claim an extended shelf beyond this limit providing certain geological criteria are met.

States hold sovereign rights over seabed and subsoil resources within their continental shelf, allowing them to authorise drilling, mining, and the construction of other installations related to resource exploitation. However, other states retain the right to lay submarine cables and pipelines subject to reasonable coastal state conditions related to resource and environmental protection.

For Analysts: Continental shelves can substantially expand a state’s access to offshore hydrocarbons and strategic minerals as well as facilitating deep-sea exploration. In regions such as the Arctic and parts of the Atlantic and Indian Oceans, extended shelf submissions are used to add weight to territorial claims and have become an increasingly significant weapon in long-term strategic competition.

The Truman Proclamation: In 1945, the Truman Proclamation declared that natural resources of the continental shelf beneath the high seas adjoining the United States were subject to US jurisdiction and control, while the waters above remained high seas. While controversial, these assertions were not reversed through international litigation and gradually became accepted practice.

This practice formed the basis of a new customary rule, codified in the 1958 Continental Shelf Convention and developed further under UNCLOS. Read more.

All parts of the ocean lying beyond any level of national jurisdiction are classed as the high seas. They cover the majority of the world’s oceans and form the largest single maritime zone under UNCLOS.

All states, whether coastal or landlocked, have freedom of navigation and overflight, as well as the right to lay submarine cables and pipelines, conduct fishing and undertake scientific research. Naval operations are fully permitted and do not require any consent.

Restrictions are limited but significant. No state may claim sovereignty over any part of the high seas, and certain activities are constrained by environmental obligations. Piracy, slavery, unauthorised broadcasting, and illicit trafficking is not permitted on the high seas, and enforcement relies on cooperation between states.

For Analysts: On paper UNCLOS provides a legal framework governing activity on the high seas. In reality, capacity, presence, and power determine how stringently it is enforced. As jurisdiction generally resides with a ship’s flag state rather than the location of illicit activity, weak or absent flag state control can facilitate its proliferation.

The high seas are a key component of global trade, data flows, and military mobility. At the same time, they are increasingly congested and contested, with major powers using naval presence and operational behaviour to signal resolve and re-establish geopolitical norms. Disputes can arise over the scope of military activity, intelligence collection, and interference with seabed infrastructure such as undersea cables.

Cold War Naval Operations: During the Cold War, American and Soviet warships and aircraft regularly operated close to one another on the high seas. Dangerous manoeuvres, simulated attacks and surveillance flights created a growing risk of collision or escalation.

Rather than restricting where their forces could operate, the two countries signed the 1972 Incidents at Sea Agreement, which laid down rules for safer encounters while leaving their navigational and operational freedoms intact. Read more.

“The Area” is defined as any area of seabed, ocean floor, and subsoil lying beyond the limits of national jurisdiction. It covers around half the Earth’s surface and is treated as a distinct legal space. The Area and its resources are designated as the common heritage of mankind under UNCLOS, meaning no state can claim sovereignty or rights over any part of it.

Activities in the Area are conducted under international administration rather than national control, primarily through the International Seabed Authority (ISA). States and state-sponsored entities may conduct exploration and, potentially, exploitation of seabed minerals, but only with authorisation from the ISA and subject to environmental obligations and benefit-sharing arrangements.

Scientific research is permitted, though the line between research and commercially relevant surveying has become increasingly blurred. Fishing and navigation are governed by high seas rules, as the Area concerns only the seabed and subsoil, not the water column above.

For Analysts: The Area should be viewed as a long-term strategic frontier as opposed to an immediate resource base. States view participation in its governance as a way to secure future access to critical minerals and influence regulatory standards and the management of global commons.

Decisions taken within this framework are likely to have lasting implications for industrial policy, environmental protection, and the credibility of multilateral governance over shared spaces. Whether states accept and comply with these rules may also provide a test case for future agreements governing other areas beyond national jurisdiction, including the Moon and outer space.

Disputes will become increasingly likely if advances in exploration and exploitation technology outpace legislation related to deep-sea mining, environmental risk management, and benefit-sharing between developed and developing states. The absence of commercial mining to date has not prevented strategic competition over access and positioning.

Malta’s Deep Seabed Initiative: In 1967, Malta’s UN ambassador, Arvid Pardo, warned that technologically advanced countries could monopolise minerals found on the deep seabed. He proposed that the seabed beyond national jurisdiction should be managed for the benefit of all countries.

The proposal helped launch the negotiations that produced UNCLOS. The Convention designated this seabed, known as “the Area”, and its resources as the common heritage of mankind and placed mineral activities there under the International Seabed Authority. Read more.

The term “International waters” is widely used to describe areas of the sea beyond any state’s territorial waters. It generally refers to waters where foreign ships retain freedom of navigation, but it is not a formal maritime zone defined by UNCLOS. Depending on the context, the term may include both exclusive economic zones and the high seas.

This distinction is important as these areas are governed by different rules. Coastal states control resources within their EEZs, while the high seas are open to all states. Therefore, while international waters remains a useful everyday expression, it should be avoided in formal reporting in favour of a the precise nomenclature of the maritime zone in question as defined by UNCLOS.

From the 18th century through the early 20th century, many states recognised a three-nautical-mile territorial sea, derived from the so-called cannon shot rule: a state’s sovereignty extended as far as it could defend its coast with shore-based artillery. This informal standard shaped maritime practice during the age of sail and early steam power, providing a narrow belt of coastal control while preserving broad freedom of navigation beyond it.

The rule was never universally codified, and states applied it unevenly as technology advanced. Its gradual erosion reflected growing coastal security concerns and expanding offshore economic interests, setting the stage for territorial seas to be codified later on under post-war law of the sea frameworks.