International waters, often called the high seas, begin 200 nautical miles (about 230 standard miles) from the U.S. coastline. That’s where the country’s Exclusive Economic Zone ends and no single nation has jurisdiction over the water. But the picture is more layered than a single boundary line. The U.S. actually has several overlapping maritime zones, each with different legal authority, and the one that matters depends on what you’re asking about: fishing, criminal law, customs enforcement, or full sovereignty.
The 12-Mile Territorial Sea
The U.S. territorial sea extends 12 nautical miles from the coast. Within this zone, the United States has full sovereignty, much like it does over land. Federal and state laws apply, the Coast Guard has complete authority, and foreign vessels must follow U.S. rules. Criminal jurisdiction under federal law reaches the full 12 miles.
This 12-mile limit has been in place since 1988, when President Reagan signed Presidential Proclamation 5928 extending it from the previous 3-mile boundary. Before that, U.S. territorial waters only reached 3 nautical miles, and some federal statutes still reference that older limit for specific regulatory purposes.
Where Measurement Starts
All these distances are measured from what’s called the “baseline,” which is the mean lower low water line along the coast as shown on NOAA’s official nautical charts. In plain terms, it’s roughly the low-tide mark. For river mouths, the baseline is a straight line drawn across the opening between the low-water points on each bank. For bays, a straight line can be drawn across the entrance if the opening is 24 nautical miles or less, which means large bays like the Chesapeake effectively push the starting point of all maritime zones farther out to sea.
The Contiguous Zone: 12 to 24 Miles
Beyond the territorial sea lies the contiguous zone, stretching from 12 to 24 nautical miles offshore. The U.S. doesn’t have full sovereignty here, but it can enforce customs, immigration, and sanitation laws. If someone is smuggling goods toward the coast or violating immigration rules, federal authorities can act within this buffer zone to prevent violations before they reach U.S. territory.
The Exclusive Economic Zone: Out to 200 Miles
The Exclusive Economic Zone, or EEZ, extends up to 200 nautical miles from the baseline. Within this enormous stretch of ocean, the U.S. holds sovereign rights over all natural resources: fish, oil, gas, minerals on the seafloor, and even energy production from wind and currents. Foreign vessels can pass through freely, but they can’t fish, drill, or extract resources without permission.
The U.S. EEZ is one of the largest in the world because it includes waters around not just the mainland coasts but also Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, the Northern Mariana Islands, and other territories scattered across the Pacific. Combined, these zones cover millions of square miles of ocean.
Where the High Seas Actually Begin
Under international law, the high seas are all parts of the ocean not included in any country’s EEZ, territorial sea, or internal waters. For the U.S., that means the high seas start at the 200-nautical-mile mark. Once you’re beyond that line, no country has jurisdiction over the water column. Ships on the high seas are governed by the laws of the country whose flag they fly.
There’s an important nuance here. Even though the U.S. has never formally ratified the United Nations Convention on the Law of the Sea (UNCLOS), the treaty that codifies most of these boundaries, it follows the convention’s rules in practice. In 1983, President Reagan declared that the U.S. would accept UNCLOS provisions on traditional ocean uses like navigation and overflight. The Senate Foreign Relations Committee has voted in favor of joining the convention multiple times, most recently in 2007 by a 17-4 margin, but the full Senate has never held a ratification vote.
State Waters vs. Federal Waters
If you’re a boater or angler, you may care more about a different boundary: where state jurisdiction ends and federal jurisdiction begins. Under the Submerged Lands Act, most coastal states control the waters and seabed from shore out to 3 nautical miles. Three exceptions exist: Texas, the Gulf coast of Florida, and Puerto Rico each control waters out to 9 nautical miles due to historical claims that predate their current political status.
This distinction matters for fishing regulations, oil and gas leasing, and environmental rules. If you’re fishing 5 miles off the coast of Alabama, you’re in federal waters and need to follow federal regulations. Five miles off the Texas coast, you’re still in state waters under Texas rules.
A Quick Reference by Distance
- 0 to 3 nautical miles: State waters for most states (9 miles for Texas, Gulf Florida, and Puerto Rico)
- 0 to 12 nautical miles: U.S. territorial sea with full sovereignty
- 12 to 24 nautical miles: Contiguous zone where customs, immigration, and pollution laws are enforced
- 12 to 200 nautical miles: Exclusive Economic Zone with resource rights
- Beyond 200 nautical miles: High seas, or true international waters
One nautical mile equals about 1.15 standard miles, so the 12-mile territorial sea is roughly 13.8 land miles, and the 200-mile EEZ boundary sits about 230 land miles offshore. For most practical purposes, if someone refers to “international waters” as the place where U.S. law no longer applies at all, they’re talking about that 200-mile line. If they mean the boundary where the U.S. no longer has complete sovereignty over everything, including passing ships, that’s the 12-mile mark.