International waters begin 12 nautical miles (about 22.2 kilometers) from a country’s coastline. Beyond that line, no single nation has sovereignty over the ocean. This boundary is established by the United Nations Convention on the Law of the Sea (UNCLOS), the global treaty that governs how countries divide up the ocean. But the full picture is more layered than a single line on a map, because coastal nations hold different levels of authority at different distances from shore.
The 12-Mile Line: Where Sovereignty Ends
Every coastal country can claim a territorial sea extending up to 12 nautical miles from its baseline. Within this zone, a nation has full sovereignty. Its laws apply to the water, the seabed beneath it, and even the airspace above it. The FAA, for example, classifies airspace beyond 12 nautical miles off the U.S. coast as international airspace.
Foreign vessels do have the right to pass through another country’s territorial sea, a concept called “innocent passage.” But they must travel continuously and refrain from activities like fishing, weapons testing, spying, or launching aircraft. If a ship violates those conditions, the coastal nation can intervene.
Where the 12 Miles Are Measured From
The 12-mile distance isn’t measured from the beach. It starts at the “baseline,” which is typically the low-water line along the coast as shown on official nautical charts. In the United States, NOAA defines this as the mean lower low water mark, the average of the lowest daily tides. Offshore islands count too. Their own low-water lines push the baseline, and therefore the territorial sea, farther out.
Certain geographic features shift the baseline in less obvious ways. Where a coastline is deeply jagged or fringed with islands, a country can draw straight lines connecting points along the coast instead of tracing every inlet. River mouths use a straight line between the low-water marks on each bank. Bays can be enclosed with a line across their entrance, as long as that line doesn’t exceed 24 nautical miles. Reefs, harbors with permanent structures like jetties, and even some features that are only exposed at low tide can all extend where the baseline sits.
These rules matter because they determine where every maritime zone begins. A country with a complex coastline or many islands can end up with territorial waters that reach much farther from shore than you might expect by looking at a map.
The Zones Between Shore and Open Ocean
The ocean doesn’t jump straight from national territory to a free-for-all. Between the territorial sea and true open ocean, there are two additional zones where coastal countries retain some authority.
Contiguous Zone: 12 to 24 Nautical Miles
From 12 to 24 nautical miles (about 44.4 km), a country can enforce its customs, immigration, tax, and health regulations. This zone exists so that nations can police smuggling and illegal entry without needing to catch offenders inside the territorial sea itself. Countries can also prevent the unauthorized removal of historical or archaeological objects from the seabed in this zone.
Exclusive Economic Zone: Up to 200 Nautical Miles
The exclusive economic zone (EEZ) stretches up to 200 nautical miles (roughly 370 km) from the baseline. Within the EEZ, a coastal nation controls all natural resources: fish, oil, gas, minerals on the seabed, and even energy generated from wind and currents. But it does not have general sovereignty. Foreign ships can sail through freely, and other countries can lay submarine cables and pipelines.
So if your question is “where can a country stop me from fishing,” the answer is 200 nautical miles. If your question is “where do a country’s laws stop applying to my boat,” the answer is generally 12 nautical miles, with some enforcement rights out to 24.
The High Seas: True International Waters
The high seas are everything beyond any country’s EEZ, territorial sea, internal waters, or archipelagic waters. By international law, no nation owns these waters. They are open to all countries for navigation, fishing, scientific research, and laying cables.
This freedom comes with a catch: enforcement is thin. On the high seas, a ship generally falls under the jurisdiction of the country whose flag it flies. If a crime happens aboard a Panamanian-flagged vessel, Panama’s laws apply. There are exceptions for a handful of offenses considered so serious that any nation can step in. Piracy is the oldest example, and most legal scholars agree this principle also covers the slave trade, genocide, war crimes, and torture.
Certain activities like fishing, shipping, seabed mining, and dumping on the high seas are governed by separate international agreements. In 2023, countries finalized a new High Seas Treaty (formally the Biodiversity Beyond National Jurisdiction Agreement) aimed at protecting marine life in international waters. The United States signed it in September 2023, and President Biden sent it to the Senate for ratification in December 2024, though the Senate has not yet acted on it.
Quick Distance Reference
- Territorial sea: 0 to 12 nautical miles (0 to 22.2 km). Full national sovereignty.
- Contiguous zone: 12 to 24 nautical miles (22.2 to 44.4 km). Limited enforcement of customs, immigration, and health laws.
- Exclusive economic zone: Up to 200 nautical miles (370 km). Control over natural resources, but not general law enforcement.
- High seas: Beyond 200 nautical miles. No national jurisdiction. Flag state law applies to vessels.
One nautical mile equals exactly 1.852 kilometers, or about 1.15 regular (statute) miles. The nautical mile is based on the geometry of the Earth: it corresponds to one minute of latitude, which is why it remains the standard unit for ocean navigation and international maritime law.