Drawing the Line at Sea: Legal Frameworks and Geographic Criteria for Straight Baselines under UNCLOS

In international maritime law, every ocean boundary—from the territorial sea to the Exclusive Economic Zone (EEZ)—is measured from a fundamental starting point: the baseline. While the default standard is the normal baseline, which follows the low-water line along the coast, nature rarely provides perfectly smooth geographical outlines. Jagged fjords, complex archipelagos, and deep coastal indentations complicate the straightforward application of hydrographic measurements.

To address complex geographical realities, international law permits coastal States to draw straight baselines under specific, strictly defined conditions. Governed primarily by Article 7 of the United Nations Convention on the Law of the Sea (UNCLOS), the method of straight baselines allows States to join appropriate points along the coast, transforming intricate coastal fringes into simplified reference lines. However, because straight baselines push maritime zones further seaward and enclose internal waters where coastal sovereignty is highest, their application remains one of the most controversial and frequently contested issues in ocean governance.

Normal Baselines versus Straight Baselines: Defining the Foundation

To understand straight baselines, one must first examine the legal baseline from which all maritime zones are measured. Under Article 5 of UNCLOS, the normal baseline for measuring the breadth of the territorial sea is the low-water line along the coast, as marked on large-scale charts officially recognized by the coastal State. This rule reflects the natural interaction between land and water, ensuring that a State's maritime boundaries closely conform to its actual physical geography.

However, applying a normal baseline across highly fragmented or indented coasts presents severe practical and administrative challenges. Following every curve of a deeply fjorded coastline would result in an exceedingly complex, outer territorial sea boundary, full of deep pockets and enclaves that complicate navigation, law enforcement, and resource management.

A straight baseline system resolves this by connecting salient points on the coast or offshore features with straight line segments. The waters lying on the landward side of these straight baselines are classified as internal waters, where the coastal State exercises full territorial sovereignty without the automatic right of innocent passage that foreign vessels enjoy in the territorial sea (subject to specific exceptions under UNCLOS Article 8).

The Genesis of the Legal Framework: The 1951 Anglo-Norwegian Fisheries Case

The modern legal doctrine of straight baselines was established before UNCLOS was drafted. Its primary origin lies in the landmark judgment delivered by the International Court of Justice (ICJ) in the Fisheries Case (United Kingdom v. Norway) in 1951.

Norway's mainland coast is exceptionally rugged, deeply carved by fjords, and fringed by a continuous continuous rampart of thousands of islands, islets, and rocks known as the skj\u00e6rgaard (rock rampart). In 1935, Norway issued a royal decree establishing a system of straight baselines connecting outer points of the skj\u00e6rgaard to protect its historic fishing grounds from foreign trawlers. The United Kingdom challenged this system, arguing that international law required baselines to follow the low-water mark of the mainland.

The ICJ ruled in favor of Norway, holding that the straight baseline method was not contrary to international law provided certain geographic criteria were respected. The Court recognized that geography must be considered as a whole, stating that maritime boundaries must not depart to any appreciable extent from the general direction of the coast and that the enclosed waters must be sufficiently closely linked to the land domain. These jurisprudential principles were subsequently codified in the 1958 Geneva Convention on the Territorial Sea and the Contiguous Zone, and later incorporated directly into Article 7 of UNCLOS.

The Legal Mechanics of UNCLOS Article 7: Conditions for Drawing Straight Baselines

UNCLOS Article 7 sets out explicit criteria that a coastal State must fulfill before employing a straight baseline system. The convention does not grant an unfettered right to draw straight lines along any coastline; rather, it establishes a conditional legal framework designed to balance coastal sovereignty with the freedoms of international navigation.

1. Deep Indentations and Cut-Into Coasts

Article 7(1) provides the first alternative geographic justification: a straight baseline system may be employed \"in localities where the coastline is deeply indented and cut into.\"

To satisfy this test, the coastal geography must exhibit more than minor curvature or gentle bays. The coastline must feature profound, continuous indentations—such as the fjords of Norway, Chile, or Western Canada—where the land and water are intricately interwoven. Merely curved coastlines do not meet this threshold.

2. Fringing Islands in the Immediate Vicinity

The second alternative under Article 7(1) applies where there is \"a fringe of islands along the coast in its immediate vicinity.\"

This criterion requires two distinct elements:

• A fringe of islands: The islands must form a cohesive, continuous chain or cluster along the coast, rather than isolated, widely dispersed islets.
• Immediate vicinity: The islands must sit in close physical proximity to the mainland coast, creating a natural spatial relationship where the islands function effectively as an extension of the mainland shore.

3. The General Direction of the Coast

Article 7(2) introduces a mandatory requirement: \"The drawing of straight baselines must not depart to any appreciable extent from the general direction of the coast.\"

This rule acts as a critical restraint against excessive claims. A State cannot construct baseline segments that project far seaward at sharp angles, creating massive geometric shapes that encompass vast expanses of open sea. The straight lines must track the macro-geographical alignment of the mainland coast.

4. Sufficient Link to the Land Domain

Article 7(3) mandates that \"the sea areas lying within the lines must be sufficiently closely linked to the land domain to be subject to the regime of internal waters.\"

This principle focuses on the character of the enclosed waters. If the waters enclosed by proposed lines display the characteristics of open ocean rather than sheltered coastal waters, the line fails the legal test. The enclosed marine areas must logically belong to the terrestrial core of the coastal State.

5. Restrictions on Low-Tide Elevations

Under Article 7(4), straight baselines cannot be drawn to or from low-tide elevations (features that are above water at low tide but submerged at high tide) unless:

• Lighthouses or similar permanent installations elevated above sea level have been built on them; or
• The drawing of baselines to and from such elevations has received general international recognition.

This rule prevents States from extending baseline systems far out to sea by anchoring lines on temporary or ephemeral geographic features that disappear beneath the tides.

Special Coastal Configurations: Rivers, Bays, and Archipelagos

Beyond Article 7, UNCLOS provides tailored rules for specific geographical formations that complement or interact with straight baselines.

Mouths of Rivers (Article 9)

If a river flows directly into the sea without forming an estuary, the baseline is a straight line drawn across the mouth of the river between points on the low-water line of its banks. If an estuary is formed, the rules governing bays under Article 10 generally apply.

Juridical Bays (Article 10)

Article 10 governs well-marked coastal indentations whose penetration is in such proportion to the width of its mouth as to contain land-locked waters. To qualify legally as a bay, an indentation must meet the mathematical semi-circle test: its area must be as large as, or larger than, that of the semi-circle whose diameter is a line drawn across the mouth of the indentation.

Furthermore, the maximum closing line across the mouth of a juridical bay cannot exceed 24 nautical miles. If the mouth exceeds 24 nautical miles, a straight closing line of 24 nautical miles may be drawn within the bay in such a manner as to enclose the maximum possible area of water.

Historic Bays and Historic Titles

Article 10(6) explicitly exempts so-called \"historic bays\" from the 24-nautical-mile limit and the semi-circle test. A historic bay is a body of water that a coastal State has treated as internal waters over a prolonged period with the open, continuous, and effective exercise of sovereignty, coupled with the acquiescence or lack of effective opposition from foreign States.

Archipelagic Baselines (Article 47)

A crucial distinction exists between straight baselines under Article 7 and archipelagic baselines under Article 47. Archipelagic baselines may only be drawn by an official Archipelagic State—defined under Article 46 as a State constituted wholly by one or more archipelagos (such as Indonesia, the Philippines, or Fiji).

Continental States that possess offshore archipelagos (such as Ecuador's Gal\u00e1pagos Islands or Portugal's Azores) cannot utilize Article 47. They must apply Article 7 straight baselines, provided the mainland or island coast satisfies the deeply indented or fringing island tests.

Summary of UNCLOS Baseline Regimes

The following table synthesizes the distinct baseline regimes, their legal sources, and core application criteria under international law:

Legal Consequences: Internal Waters and Maritime Zone Expansions

The decision to draw straight baselines carries significant legal and geopolitics consequences because it fundamentally alters the legal regime of the enclosed waters and pushes the outer limits of all offshore maritime zones seaward.

1. Regime of Internal Waters and Preservation of Passage Rights

When a State draws a straight baseline, waters that were previously treated as territorial sea or high seas are converted into internal waters. In internal waters, the coastal State possesses absolute territorial sovereignty, including the power to prohibit foreign vessels from entering entirely.

However, to prevent States from using straight baselines to disrupt established international navigation, UNCLOS includes a critical safeguard in Article 8(2). If the establishment of a straight baseline has the effect of enclosing as internal waters areas which had not previously been considered as such, a right of innocent passage automatically persists through those newly enclosed waters.

2. Outward Push of Maritime Zones

Because all extended maritime zones are measured from the baseline, every nautical mile that a straight baseline moves seaward pushes the outer boundaries of the State's maritime zones equal distances into the ocean:

• Territorial Sea: Up to 12 nautical miles from the baseline.
• Contiguous Zone: Up to 24 nautical miles from the baseline.
• Exclusive Economic Zone (EEZ): Up to 200 nautical miles from the baseline.
• Continental Shelf: Up to 200 nautical miles (or up to 350 nautical miles / 100 nautical miles beyond the 2,500-meter isobath under extended continental shelf formulas).

By connecting offshore points, a State can enclose vast marine areas, securing exclusive sovereign rights over fisheries, oil and gas deposits, and seabed minerals within expanded EEZ and continental shelf limits.

State Practice, Excessive Baseline Claims, and Diplomatic Friction

Because straight baselines offer significant geographic and resource advantages, coastal States face an inherent incentive to stretch the legal parameters of Article 7. Over the past several decades, excessive baseline claims have become a primary source of maritime friction worldwide.

Common Forms of Excessive Claims

State practice demonstrates several recurring misapplications of Article 7:

• Smoothing Smooth Coasts: Drawing straight baselines along relatively straight or gently curved coastlines that lack deep indentations or island fringes.
• Connecting Distant Islands: Linking isolated, far-flung offshore islands that do not form a true "fringe in the immediate vicinity" of the coast.
• Excessive Segment Lengths: Constructing exceptionally long baseline segments—sometimes exceeding 100 nautical miles—that bypass open ocean areas and depart radically from the general direction of the coast.
• Improper Use of Low-Tide Elevations: Anchoring baselines on low-tide elevations that lack permanent lighthouses or installations.

Diplomatic Responses and Freedom of Navigation

Maritime nations—particularly maritime trading States and naval powers—frequently issue formal diplomatic protests against excessive straight baselines. The United States, through its Freedom of Navigation (FON) Program, routinely conducts operational challenges and diplomatic protests against straight baseline claims that it deems non-compliant with UNCLOS Article 7.

International courts and arbitral tribunals have consistently emphasized that a State's unilateral declaration of a baseline is not self-legitimizing. As the ICJ stated in the 1951 Fisheries Case, \"The delimitation of sea areas has always an international aspect; it cannot depend merely upon the will of the coastal State as expressed in its municipal law.\"

Contemporary Challenges: Sea-Level Rise and Ambulatory Baselines

As climate change accelerates global sea-level rise, the law of baselines faces unprecedented structural challenges. Traditionally, baselines under UNCLOS are considered ambulatory—meaning that as the low-water line moves landward due to coastal erosion and rising sea levels, the baseline moves landward as well, shrinking the State's outer maritime zones.

For low-lying coastal States and small island developing States (SIDS), this physical reality poses an existential threat. If sea levels submerge fringing islands or smooth out coastal features, States risk losing their legal entitlement to straight baselines or having their entire maritime boundaries contract.

To combat this, international legal bodies—including the International Law Association (ILA) and the International Law Commission (ILC)—along with regional organizations like the Pacific Islands Forum, are championing the legal concept of fixed baselines. Under this emerging practice, once a coastal State establishes and deposits its straight baselines with the Secretary-General of the United Nations in accordance with UNCLOS, those coordinates would remain fixed permanently, regardless of physical coastline changes caused by sea-level rise.

Conclusion: Maintaining the Equilibrium of the Law of the Sea

The rules governing straight baselines under UNCLOS Article 7 represent a delicate legal compromise between geographical reality and international rights. By allowing coastal States to draw straight baselines across deeply indented coasts and island fringes, international law accommodates genuine geographical complexities that make normal baselines unworkable.

At the same time, the strict legal prerequisites—requiring compliance with the general direction of the coast, proximity of island fringes, and protection of innocent passage—serve as indispensable safeguards against coastal enclosure. As maritime activities intensify and climate change reshapes global coastlines, rigorous adherence to the legal criteria of straight baselines remains fundamental to preserving stable maritime boundaries and safeguarding the freedom of the seas.