UNCLOS Maritime Zones, Innocent Passage and Hot Pursuit

Read first: Flag State, Port State, Coastal State and Classification Societies. This topic shows where each coastal State’s power starts and stops at sea, and what a passing ship may and may not do.

The Zones at a Glance

In short: UNCLOS (the United Nations Convention on the Law of the Sea, 1982) splits the sea into zones. Every zone is measured from the baseline, and the further out you go, the less power the coastal State has.

• The 12 / 24 / 200 NM figures are maximums. A State may claim less, and where two coasts are close, the zones meet at an agreed line or a median line.
• On the bridge: the chart shows the limits of national claims, and the Annual Notices to Mariners include a notice on national claims to maritime jurisdiction (territorial sea, contiguous zone, EEZ) — see Chart Correction and Notices to Mariners.

Baselines and Internal Waters

In short: the baseline is the line from which every zone is measured. Waters on the land side of it are internal waters.

• The baseline is an imaginary line: it marks where the State’s maritime jurisdiction begins.
• Normal baseline: the low-water line along the coast, as marked on large-scale charts officially recognised by the coastal State (UNCLOS Art. 5). See Chart Projections, Scales and Datums for why the low-water line sits on the chart.
• Straight baselines: where the coast is deeply indented or has a fringe of islands close to it, the State may join suitable points with straight lines (UNCLOS Art. 7). They are set by the State’s law.
• Internal waters = everything landward of the baseline: ports, harbours, many bays and river mouths (UNCLOS Art. 8).
  • The State has full sovereignty, just as on land. A foreign ship has no general right of innocent passage there.
  • Exception: where a new straight baseline encloses waters that were not internal before, innocent passage still applies there (UNCLOS Art. 8).
• Remember: all maritime zones are measured from the baseline, never from the shoreline you see.

The Territorial Sea

In short: a belt of sea up to 12 NM wide from the baseline, where the coastal State has sovereignty — but foreign ships keep the right of innocent passage.

• Breadth: up to 12 NM from the baseline (UNCLOS Art. 3).
• Sovereignty covers the water, the seabed and subsoil and the airspace above (UNCLOS Art. 2).
• The coastal State may make laws for ships in passage on: safety of navigation and traffic, aids to navigation, cables and pipelines, fisheries, pollution, research and surveys, and customs, fiscal, immigration and sanitary matters (UNCLOS Art. 21).
• Foreign ships in passage must obey those laws and the COLREG (UNCLOS Art. 21(4)) — see COLREG Structure, Application and Definitions.
• The State may require ships to use sea lanes and traffic separation schemes — see Narrow Channels and Traffic Separation Schemes. Tankers, nuclear-powered ships and ships carrying nuclear or dangerous/noxious substances can be confined to those lanes (UNCLOS Art. 22). Nuclear ships must carry their documents and take special precautions (UNCLOS Art. 23).
• The State must publicise any danger to navigation it knows of in its territorial sea (UNCLOS Art. 24).

Innocent Passage

In short: any ship may cross a foreign territorial sea without asking permission, as long as the passage is continuous and expeditious and no threat to the coastal State’s peace, good order or security.

• Passage = crossing the territorial sea, or going to or from internal waters or a port (UNCLOS Art. 18).
  • It must be continuous and expeditious.
  • Stopping and anchoring are allowed only when part of ordinary navigation, forced by force majeure or distress, or to help people, ships or aircraft in danger.
• Innocent = not prejudicial to the peace, good order or security of the coastal State (UNCLOS Art. 19). Passage is not innocent if the ship:
  1. threatens or uses force against the State;
  2. carries out weapons exercises;
  3. collects information against the State’s defence or security;
  4. spreads propaganda against its defence or security;
  5. launches, lands or takes on board any aircraft;
  6. launches, lands or takes on board any military device;
  7. loads or unloads goods, currency or people against customs, fiscal, immigration or sanitary laws;
  8. causes wilful and serious pollution;
  9. goes fishing;
  10. carries out research or survey work;
  11. interferes with the State’s communications or installations;
  12. does anything else not directly linked to passage.
• Easy way to remember the core: no fishing, no fighting, no polluting — and no threat to the country.
• Submarines must navigate on the surface and show their flag (UNCLOS Art. 20).
• The coastal State must not hamper innocent passage. It may suspend it temporarily in specified areas when essential for its security (for example weapons exercises), without discrimination, and only after publishing it (UNCLOS Art. 25(3)).
• No charge may be levied just for passing through (UNCLOS Art. 26).
• On the bridge: a yacht crossing a foreign territorial sea that trolls a fishing line, lands a helicopter on its helideck or runs a seabed survey is no longer in innocent passage.
• Transit passage is different. In straits used for international navigation (high seas or EEZ to high seas or EEZ) all ships and aircraft have the right of transit passage: continuous and expeditious, and it cannot be suspended (UNCLOS Art. 38, UNCLOS Art. 44). Ships in transit must still follow the COLREG and pollution rules (UNCLOS Art. 39).

The Contiguous Zone

In short: a zone up to 24 NM from the baseline where the coastal State has limited powers — only to protect its customs, fiscal, immigration and sanitary laws.

• Breadth: not beyond 24 NM from the baseline (UNCLOS Art. 33). In practice it is the 12 NM band just outside the territorial sea.
• Powers: the State may take the control needed to prevent and punish breaches of its customs, fiscal, immigration or sanitary laws committed in its territory or territorial sea (UNCLOS Art. 33).
• Memory hook: CFIS — Customs, Fiscal, Immigration, Sanitary.
• Environment is not on the list. Pollution powers come from the EEZ and Part XII of UNCLOS, not from the contiguous zone.
• From here the State may start a hot pursuit, but only for a breach of the rights this zone protects (UNCLOS Art. 111(1)).

The Exclusive Economic Zone (EEZ)

In short: a zone up to 200 NM from the baseline where the coastal State owns the resources, while other ships keep the freedom of navigation.

• Breadth: not beyond 200 NM from the baseline (UNCLOS Art. 57).
• Coastal State sovereign rights: to explore, exploit, conserve and manage the natural resources, living or non-living, of the water, seabed and subsoil — and to produce energy from water, currents and winds (UNCLOS Art. 56).
• Coastal State jurisdiction over: artificial islands and installations, marine scientific research, and protection of the marine environment (UNCLOS Art. 56).
• Other States keep the freedoms of navigation, overflight and laying cables and pipelines (UNCLOS Art. 58).
• Safety zones around installations (rigs, wind turbines): normally not more than 500 m from the outer edge (UNCLOS Art. 60(5)). On the bridge: keep out of them.
• Fisheries enforcement: the State may board, inspect, arrest and prosecute; a seized vessel and crew must be released promptly once a reasonable bond is posted (UNCLOS Art. 73).
• Pollution: with clear grounds, the State may ask a passing ship for her identity, port of registry, last and next port (UNCLOS Art. 220(3)).

The Continental Shelf

In short: the seabed and subsoil beyond the territorial sea, out to the edge of the continental margin. It is very rich in resources (oil, gas, minerals), and they belong to the coastal State.

• Extent: the natural prolongation of the land to the outer edge of the continental margin, or 200 NM from the baseline where the margin is shorter (UNCLOS Art. 76(1)).
• Outer limit: not more than 350 NM from the baseline, or not more than 100 NM beyond the 2,500 m isobath (UNCLOS Art. 76(5)).
• Rights: sovereign and exclusive rights to explore and exploit its natural resources. Nobody else may do so without the State’s express consent (UNCLOS Art. 77).
• The rights exist automatically: no occupation and no proclamation needed (UNCLOS Art. 77(3)).
• They cover only the seabed and subsoil: the water and airspace above keep their own status, EEZ or high seas (UNCLOS Art. 78).

The High Seas

In short: all the sea beyond any EEZ, territorial sea, internal or archipelagic waters. It belongs to no State and is open to all.

• Scope: all parts of the sea not in an EEZ, territorial sea, internal waters or archipelagic waters (UNCLOS Art. 86).
• No State may subject any part of the high seas to its sovereignty (UNCLOS Art. 89).
• Freedoms for all States, coastal or land-locked (UNCLOS Art. 87): navigation, overflight, cables and pipelines, artificial islands, fishing, scientific research.
• A ship sails under one flag only and, on the high seas, is under the exclusive jurisdiction of her flag State (UNCLOS Art. 92).
• A warship may board a foreign ship only on reasonable suspicion of piracy, slave trade, unauthorised broadcasting, no nationality, or false/hidden flag (UNCLOS Art. 110).
• Every master must render assistance to anyone in danger of being lost at sea, if it can be done without serious danger to own ship and people (UNCLOS Art. 98) — see Distress Signals.

Archipelagic States

In short: a State made entirely of one or more archipelagos may draw straight archipelagic baselines around its outer islands. The water inside becomes archipelagic waters, under its sovereignty, but ships keep passage rights.

• Archipelagic State = a State made up wholly of one or more archipelagos (UNCLOS Art. 46). Examples: Indonesia, the Philippines.
• Archipelagic baselines join the outermost points of the outermost islands and drying reefs (UNCLOS Art. 47):
  • water-to-land ratio inside: between 1:1 and 9:1;
  • each baseline not more than 100 NM; up to 3 % of them may reach 125 NM.
• Archipelagic waters: sovereignty over the water, seabed, subsoil and airspace, whatever the depth or distance from the coast (UNCLOS Art. 49).
• Foreign ships have innocent passage through archipelagic waters (UNCLOS Art. 52) and archipelagic sea lanes passage in designated lanes: normal mode, continuous, expeditious and unobstructed (UNCLOS Art. 53).
• The territorial sea, contiguous zone and EEZ are then measured from the archipelagic baselines.

Conservation Zones and the Marine Environment

In short: protecting the sea is a universal obligation, and coastal States set conservation zones for fish stocks and fragile ecosystems.

• All States have the obligation to protect and preserve the marine environment (UNCLOS Art. 192). It applies everywhere, high seas included.
• Measures must protect rare or fragile ecosystems and the habitat of depleted, threatened or endangered species (UNCLOS Art. 194(5)).
• In its EEZ the coastal State fixes the allowable catch and takes conservation measures so that stocks are not endangered by over-exploitation (UNCLOS Art. 61). These fishery or conservation zones often have their own limits, marked on charts and in sailing directions.
• Example: Malta keeps a Fisheries Management Conservation Zone out to 25 NM (see Malta below).

Hot Pursuit

In short: a coastal State may chase a foreign ship that has broken its laws out onto the high seas and arrest her there — as long as the chase starts in its waters, never stops, and ends when the ship reaches another State’s territorial sea.

• When: the authorities have good reason to believe the ship has broken the coastal State’s laws (UNCLOS Art. 111(1)).
• Where it must start: while the ship (or one of her boats) is in internal waters, archipelagic waters, the territorial sea or the contiguous zone. From the contiguous zone only for breaches of CFIS rights; from the EEZ or continental shelf only for breaches of the laws that apply there, safety zones included (UNCLOS Art. 111(1)–(2)).
• Signal first: a visual or sound signal to stop, given from a distance at which the ship can see or hear it (UNCLOS Art. 111(4)).
• Who may chase: only warships, military aircraft or other ships/aircraft clearly marked as on government service and authorised to do so (UNCLOS Art. 111(5)).
• Continuous: the pursuit may go beyond the zone only if it is not interrupted. An aircraft that starts it must keep on until a ship or aircraft of the State takes over (UNCLOS Art. 111(1), UNCLOS Art. 111(6)).
• Ends: as soon as the pursued ship enters the territorial sea of her own State or of a third State (UNCLOS Art. 111(3)). Reaching the high seas does not end it.
• A ship stopped or arrested outside the territorial sea without justification is entitled to compensation (UNCLOS Art. 111(8)).
• On the bridge: a patrol boat signals a trawler fishing illegally 15 NM off the coast (inside the EEZ). She runs. The patrol may chase her non-stop across the high seas, but must stop once she enters a neighbour’s 12 NM.

Malta’s Maritime Zones

In short: Malta uses the standard UNCLOS limits, plus a 25 NM fisheries zone. In the narrow central Mediterranean, its outer limits meet those of its neighbours.

• Territorial waters: 12 NM; contiguous zone: 24 NM (Territorial Waters and Contiguous Zone Act, Cap. 226; EU Maritime Spatial Planning platform).
• Fisheries Management Conservation Zone: 25 NM from the baseline (EU Maritime Spatial Planning platform).
• Exclusive Economic Zone Act (Cap. 625, 2021): lets the Government designate an EEZ and environment protection areas. Where a neighbour’s coast is opposite, the boundary is set by agreement or, without one, at the median line. Safety zones around installations: 500 m.
• Continental shelf: under the Continental Shelf Act (Cap. 535).