Territorial sovereignty over ocean waters

 Oceans are international but nations have territorial sovereignty how far off shore?

Under the international treaty known as the United Nations Convention on the Law of the Sea (UNCLOS), a nation's absolute territorial sovereignty extends up to 12 nautical miles (about 13.8 miles or 22.2 kilometers) from its coastal baseline. 

However, ocean jurisdiction does not just stop at 12 miles. International law breaks the ocean down into progressive zones, gradually scaling back a country's control the further out you go. 

The 4 Major Maritime Zones

[ Land ] |--- 12 nm ---|--- 24 nm ---|------------------- 200 nm -------------------|

         | Territorial | Contiguous  |            Exclusive Economic                |
         |    Sea      |    Zone     |                Zone (EEZ)                    | High Seas ->

• Territorial Sea (0 to 12 nautical miles): This is considered sovereign territory. The coastal nation has full sovereign control over the water column, the seabed below, and the airspace above—virtually identical to its laws on dry land. The only major caveat is the rule of innocent passage, which allows foreign ships to transit through these waters peacefully without conducting military drills, fishing, or spying. 
• Contiguous Zone (12 to 24 nautical miles): While not fully sovereign territory, a country can enforce limited laws here regarding customs, immigration, taxation, and pollution. It acts as a buffer zone to catch or deter lawbreakers before they reach the mainland. 
• Exclusive Economic Zone / EEZ (12 to 200 nautical miles): A country does not have total sovereignty here, but it has exclusive "sovereign rights" to exploit natural resources. This includes all fishing, oil and gas drilling, wind energy generation, and scientific research. However, foreign nations still retain the right to freely navigate ships and fly aircraft through the EEZ. 
• The High Seas (Beyond 200 nautical miles): These are true international waters. No single nation has any sovereign claim or exclusive rights over them. They are governed by international treaties and are open to all nations for peaceful use. 

Exceptions and Overlaps

When two countries are situated close together (like countries bordering the Mediterranean or Caribbean seas) and their 12-mile or 200-mile zones overlap, they must negotiate a median line right down the middle. Furthermore, a country can sometimes claim resource rights to the seabed past 200 miles if they can scientifically prove their continental shelf extends further out, though this does not grant them ownership of the water above it.