Maritime Zones & Ocean Boundaries
Learn how oceans are divided into maritime zones: territorial seas, exclusive economic zones, and high seas. Discover why islands matter and how countries share overlapping waters.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on Maritime Zones & Ocean Boundaries, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Oceans cover more than 70% of Earth, but they aren't free-for-all spaces. Countries have rules about which waters belong to them and which are open to everyone. These maritime zones determine who can fish where, who owns undersea resources, and what activities are legal in different parts of the ocean. Understanding these boundaries helps explain ocean disputes, fishing conflicts, and why a tiny island can suddenly give a country control over a huge area of water.
The Three Maritime Zones
Every coastal country controls three distinct zones extending outward from its shoreline. The territorial sea extends 12 nautical miles from the coast. Inside this zone, a country has almost complete control—it can enforce laws, tax activities, and exclude foreign ships (except for innocent passage, which is the right of ships to travel through without stopping). Beyond 12 nautical miles lies the exclusive economic zone (EEZ), which extends to 200 nautical miles from the coast. In the EEZ, the coastal country controls fishing rights and the right to extract resources from the seabed—like minerals, oil, and natural gas. Foreign ships can pass through, but they cannot fish or mine without permission. Everything beyond 200 nautical miles is the high seas, which belongs to no country and is open to all nations. International rules apply there, and activities like fishing require cooperation and agreement.
Why these specific distances? The 12-nautical-mile territorial sea is short enough that a country can realistically enforce its laws there. The 200-nautical-mile EEZ is based on how far technology allowed countries to exploit ocean resources when these rules were created in the 1980s. Together, they balance coastal nations' interests in controlling nearby resources with the principle that oceans should remain partly open for all humanity.
Why these specific distances? The 12-nautical-mile territorial sea is short enough that a country can realistically enforce its laws there. The 200-nautical-mile EEZ is based on how far technology allowed countries to exploit ocean resources when these rules were created in the 1980s. Together, they balance coastal nations' interests in controlling nearby resources with the principle that oceans should remain partly open for all humanity.
Islands and the Extension of Power
A small island changes everything. An island, no matter how tiny, gets its own territorial sea and exclusive economic zone. A rock barely above water can be the basis for a 200-nautical-mile circle of economic control. This creates enormous strategic and economic advantages. A single island might triple a country's ocean territory. For example, if a country has a straight coastline but also owns a distant island, that island generates a full EEZ around itself. In some regions, disputes over small islands are really disputes over the EEZs they create.
Not every rock counts. Under international law (the UN Convention on the Law of the Sea), a feature must be naturally above water at high tide and capable of supporting human life or economic activity to generate a full EEZ. Reefs and rocks that are underwater at high tide do not count. This rule exists to prevent countries from dumping artificial platforms and claiming vast ocean territory. Still, possession of a legitimate island can be transformative. This is why countries sometimes contest ownership of remote islands—the winner gains control over fisheries and mineral resources worth billions of dollars over time.
Not every rock counts. Under international law (the UN Convention on the Law of the Sea), a feature must be naturally above water at high tide and capable of supporting human life or economic activity to generate a full EEZ. Reefs and rocks that are underwater at high tide do not count. This rule exists to prevent countries from dumping artificial platforms and claiming vast ocean territory. Still, possession of a legitimate island can be transformative. This is why countries sometimes contest ownership of remote islands—the winner gains control over fisheries and mineral resources worth billions of dollars over time.
Overlapping Zones and Median Lines
When two countries' zones overlap, they cannot each claim the full 200 nautical miles. Instead, international law uses a median line (also called an equidistant line) to split the overlapping area fairly. A median line runs between two coasts so that every point on the line is equidistant from each coast. Think of it as an invisible centerline drawn on the ocean.
The median line principle works for both territorial seas and EEZs. If Country A and Country B lie less than 24 nautical miles apart, their territorial seas would overlap; a median line splits them at 12 nautical miles from each coast. If they lie less than 400 nautical miles apart, their EEZs overlap; the median line is drawn at 200 nautical miles from each coast (or halfway between, whichever is closer to each coast).
Drawing a median line on a map is more complex than on flat paper. Earth's curvature and the actual shape of the coastline matter. Bays, peninsulas, and islands all affect where the line goes. Countries often negotiate median lines to avoid dispute, but sometimes disagreement leads to conflict. Understanding median lines reveals why geography at the local scale—the exact shape of a coastline and the positions of nearby islands—can shape international relations.
The median line principle works for both territorial seas and EEZs. If Country A and Country B lie less than 24 nautical miles apart, their territorial seas would overlap; a median line splits them at 12 nautical miles from each coast. If they lie less than 400 nautical miles apart, their EEZs overlap; the median line is drawn at 200 nautical miles from each coast (or halfway between, whichever is closer to each coast).
Drawing a median line on a map is more complex than on flat paper. Earth's curvature and the actual shape of the coastline matter. Bays, peninsulas, and islands all affect where the line goes. Countries often negotiate median lines to avoid dispute, but sometimes disagreement leads to conflict. Understanding median lines reveals why geography at the local scale—the exact shape of a coastline and the positions of nearby islands—can shape international relations.
Activities and Their Zones
Different human activities are allowed in different zones. In the territorial sea, a coastal country can forbid foreign fishing, ban military exercises, regulate shipping, collect taxes on goods, and enforce environmental laws. Foreign warships have limited rights; they can pass through "without stopping" but may not conduct military maneuvers.
In the EEZ, foreign ships have much more freedom. They can navigate freely and conduct scientific research, but they cannot fish commercially or extract seabed resources without the coastal nation's permission. Submarines and warships can pass through with no notification. A foreign country's research vessel studying ocean currents or fish populations needs consent from the coastal state, though most routine research is allowed.
On the high seas, almost no country has authority. Ships from any nation can fish (though some fish stocks are regulated by international agreements). Environmental rules are weaker, and enforcement is difficult. Military activities are permitted but bound by international law. Pollution is prohibited but hard to police. The high seas remain a commons—a shared space where international cooperation is necessary because no single country is in charge.
This system reflects a compromise: coastal nations get security and economic benefit from nearby waters, while the global community retains access to ocean resources farther out. Where students go wrong: they sometimes think a country "owns" its EEZ the way it owns land. An EEZ is actually a limited zone of control—sovereignty is weaker there than in the territorial sea or on land.
In the EEZ, foreign ships have much more freedom. They can navigate freely and conduct scientific research, but they cannot fish commercially or extract seabed resources without the coastal nation's permission. Submarines and warships can pass through with no notification. A foreign country's research vessel studying ocean currents or fish populations needs consent from the coastal state, though most routine research is allowed.
On the high seas, almost no country has authority. Ships from any nation can fish (though some fish stocks are regulated by international agreements). Environmental rules are weaker, and enforcement is difficult. Military activities are permitted but bound by international law. Pollution is prohibited but hard to police. The high seas remain a commons—a shared space where international cooperation is necessary because no single country is in charge.
This system reflects a compromise: coastal nations get security and economic benefit from nearby waters, while the global community retains access to ocean resources farther out. Where students go wrong: they sometimes think a country "owns" its EEZ the way it owns land. An EEZ is actually a limited zone of control—sovereignty is weaker there than in the territorial sea or on land.
Key terms
- Territorial Sea.
- The zone extending 12 nautical miles from a coastline, where a coastal country has nearly complete control over activities, laws, and resources.
- Exclusive Economic Zone (EEZ).
- The zone extending 200 nautical miles from a coastline, where a coastal country controls fishing and seabed resource extraction but foreign ships retain navigation rights.
- High Seas.
- Ocean areas beyond 200 nautical miles from any coast; they belong to no country and are governed by international law and agreements.
- Median Line.
- An imaginary line drawn equidistant from two coasts, used to split overlapping maritime zones fairly between neighboring countries.
- Innocent Passage.
- The right of foreign ships to travel through another nation's territorial sea without stopping, provided they do not threaten security or violate laws.
- Nautical Mile.
- A unit of distance used at sea, equal to about 1.15 statute miles or 1.85 kilometers; standard for measuring maritime zones.
Worked example
Country A and Country B are separated by a strait 150 kilometers (about 81 nautical miles) wide. Country A wants to fish in the middle of the strait; Country B says the fish belong to it. Using the maritime zone system, explain why Country B is wrong and where the median line falls.
Step 1: Convert the distance to nautical miles if not already done. The strait is 81 nautical miles wide.
Step 2: Identify which zones overlap. Since the strait is 81 nautical miles wide, it is wider than 24 nautical miles (twice the territorial sea). This means the two countries' territorial seas (12 nautical miles each) do not overlap—there is open water between them. However, the strait is less than 400 nautical miles wide, so the two countries' exclusive economic zones (200 nautical miles each) definitely overlap.
Step 3: Apply the median line rule. Because the EEZs overlap, a median line must be drawn. The median line is drawn at a distance equidistant from both coasts. Since the strait is 81 nautical miles wide, the median line is drawn at 40.5 nautical miles from Country A's coast and 40.5 nautical miles from Country B's coast.
Step 4: Answer the question. At 40.5 nautical miles from the coast, the fishing area is in both countries' EEZs, but it is on Country A's side of the median line. Therefore, Country A has the right to fish there. Country B has no special claim to that part of the strait because it lies outside the 200-nautical-mile zone where both countries overlap. Country B controls only the area on its side of the median line.
Conclusion: The median line principle ensures that each country gets equal access to overlapping EEZs. Country A is correct.
Step 2: Identify which zones overlap. Since the strait is 81 nautical miles wide, it is wider than 24 nautical miles (twice the territorial sea). This means the two countries' territorial seas (12 nautical miles each) do not overlap—there is open water between them. However, the strait is less than 400 nautical miles wide, so the two countries' exclusive economic zones (200 nautical miles each) definitely overlap.
Step 3: Apply the median line rule. Because the EEZs overlap, a median line must be drawn. The median line is drawn at a distance equidistant from both coasts. Since the strait is 81 nautical miles wide, the median line is drawn at 40.5 nautical miles from Country A's coast and 40.5 nautical miles from Country B's coast.
Step 4: Answer the question. At 40.5 nautical miles from the coast, the fishing area is in both countries' EEZs, but it is on Country A's side of the median line. Therefore, Country A has the right to fish there. Country B has no special claim to that part of the strait because it lies outside the 200-nautical-mile zone where both countries overlap. Country B controls only the area on its side of the median line.
Conclusion: The median line principle ensures that each country gets equal access to overlapping EEZs. Country A is correct.
Practice questions
A small island nation owns a single rocky island that is naturally above water and has been inhabited by a small population for decades. Which statement best describes the maritime zones this island generates?
- The island generates only a territorial sea because it is too small to support an EEZ.
- The island generates both a 12-nautical-mile territorial sea and a 200-nautical-mile exclusive economic zone.
- The island generates a territorial sea only if more than 100 people live there.
- The island cannot generate any zones because it is an island, not a continent.
Answer: The island generates both a 12-nautical-mile territorial sea and a 200-nautical-mile exclusive economic zone.
Under international law, any naturally formed island above water at high tide that can support human life or economic activity generates a full maritime zone. This includes a 12-nautical-mile territorial sea and a 200-nautical-mile exclusive economic zone. The size of the island and the size of its population do not matter. This principle is why small island nations have significant ocean territory and why disputes over remote islands can be economically important. The island itself is small, but the zones it generates are enormous.
Two countries share a border on the ocean 160 nautical miles apart. Their EEZs overlap. Using a median line, approximately how many nautical miles from Country A's coast does the median line fall?
- 12 nautical miles
- 40 nautical miles
- 80 nautical miles
- 160 nautical miles
Answer: 80 nautical miles
When two countries are 160 nautical miles apart and their EEZs overlap, the median line is drawn equidistant from both coasts. Equidistant means halfway between them. The halfway point between 0 (Country A's coast) and 160 (Country B's coast) is 80 nautical miles from Country A's coast. This means Country A controls fishing rights from its coast to the 80-nautical-mile mark, and Country B controls fishing rights from the median line to its own coast. Each country gets an equal share of the overlapping zone.
Explain why a coastal country cannot prohibit foreign warships from passing through its exclusive economic zone, even though it controls fishing in that zone. What does this tell you about the difference between the territorial sea and the EEZ?
Answer: A complete answer will note that the EEZ gives a country control over living and non-living resources (fishing, minerals, oil), not complete sovereignty. Foreign warships have navigation rights in the EEZ, which means they can pass through freely. In the territorial sea, by contrast, a country has nearly complete control and can enforce more restrictions on foreign military activity. This shows that an EEZ is a limited zone for resource control, not full ownership of the ocean. It reflects a balance between coastal nations' economic interests and the international principle that ocean space should remain open for passage and research.
This question asks students to reason about the structure of maritime law. The answer reveals a key distinction: territorial seas are about security and control of nearby waters, while EEZs are specifically about resource rights. Foreign warships can pass through the EEZ because the zone does not grant the coastal country military or political sovereignty—it grants economic rights. This is an important concept that prevents maritime zones from becoming closed-off territories and preserves freedom of navigation on the world's oceans. Students who answer this correctly show they understand the purpose of each zone, not just its distance.
FAQ
- Why is 200 nautical miles the distance for an EEZ and not some other number?
- The 200-nautical-mile distance was set based on the technology available in the 1980s when the UN Convention on the Law of the Sea was created. At that time, countries could realistically extract resources (fish, oil, minerals) up to about that distance using available technology. It was a practical compromise. Today, technology can reach farther, but 200 nautical miles remains the standard. It balances giving coastal countries meaningful control over nearby resources while keeping parts of the ocean open and shared.
- Can a country create artificial islands and claim an EEZ around them?
- No. International law says that only naturally formed islands—features that are above water at high tide and capable of supporting human life or economic activity—generate maritime zones. Artificial structures, platforms, and man-made islands do not. This rule exists to prevent countries from dumping rocks or building structures in the middle of the ocean just to claim vast areas. Without this rule, any wealthy nation could expand its territory indefinitely by building artificial islands, which would be unfair and chaotic.
- What happens if two countries disagree about where the median line should be drawn between them?
- They try to negotiate an agreement. Many countries have signed treaties that define median lines in their overlapping zones. If negotiation fails, they may take the dispute to international courts or use mediation. In rare cases, disagreement can lead to conflict, though most nations prefer to resolve maritime disputes through diplomacy. The dispute over the South China Sea is an example where multiple countries disagree about maritime boundaries, and the resolution process remains ongoing. International law provides the framework, but countries must work out the details themselves.
- Do submarines have to ask permission to pass through a country's EEZ?
- No. Submarines, like any other warships or foreign vessels, have the right to navigate freely through the EEZ. They do not need to announce themselves or ask permission. This is one of the key ways the EEZ differs from the territorial sea. In the territorial sea, foreign submarines are technically not allowed to submerge—they must travel on the surface. In the EEZ, they can move freely, submerged or not. This principle protects the rights of all nations to move through ocean space without obstruction.
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