A coastal state is any sovereign nation or subnational state that borders an ocean, sea, or other major body of water. The term carries weight in both international law and U.S. domestic policy, where it determines everything from territorial boundaries at sea to eligibility for federal coastal management funding. Out of roughly 193 sovereign nations, about 149 are coastal states, while 44 are landlocked.
The International Law Definition
Under the United Nations Convention on the Law of the Sea (UNCLOS), a coastal state’s sovereignty extends beyond its land territory into an adjacent belt of sea called the territorial sea. That sovereignty covers the water itself, the airspace above it, and the seabed and subsoil beneath it. This gives coastal states the legal authority to adopt laws governing passage through their waters, enforce customs and immigration rules, and take steps to prevent unauthorized entry.
Coastal states can also regulate what happens in several concentric zones radiating outward from their shoreline, each with different levels of authority:
- Territorial sea (0 to 12 nautical miles): Full sovereignty. The coastal state controls nearly all activity, though foreign ships retain a right of “innocent passage,” meaning they can transit peacefully without stopping.
- Contiguous zone (12 to 24 nautical miles): More limited authority. The coastal state can enforce customs, tax, immigration, and sanitation laws but doesn’t have full sovereignty over the water.
- Exclusive economic zone, or EEZ (up to 200 nautical miles): The coastal state has exclusive rights to explore, exploit, and manage natural resources, including fish stocks, oil, and minerals on the seabed. Other nations can still navigate and lay cables through this zone.
Within its internal waters and ports, a coastal state is fully sovereign. It can place any conditions it wants on access to its ports, with the narrow exception of ships in extreme emergency.
Coastal States in the United States
In the U.S., the term “coastal state” has a specific legal definition that’s broader than you might expect. Federal law defines it as any state bordering the Atlantic, Pacific, or Arctic Ocean, the Gulf of Mexico, Long Island Sound, or one or more of the Great Lakes. That means states like Ohio, Wisconsin, Minnesota, and Illinois qualify as coastal states alongside Florida and California. Puerto Rico, the U.S. Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands also count.
In total, NOAA’s Office for Coastal Management works with 30 states and several territories under this classification. The practical consequence is that Great Lakes states are eligible for the same federal coastal management programs, research reserves, and resilience funding as states with ocean shorelines.
Why the Designation Matters Economically
Coastal areas are economic engines. In the U.S., coastal shoreline counties account for 46 percent of the nation’s GDP and provide 39 percent of all jobs, despite covering a relatively small share of the country’s land area. About 87 million people, or 29 percent of the U.S. population, live in coastline counties. That population has grown dramatically over the past several decades, rising from 47.4 million in 1960 to 87.4 million by 2008, an 84 percent increase.
This concentration of people and economic activity is exactly why Congress passed the Coastal Zone Management Act in 1972. The law, administered by NOAA, created a framework for states to balance competing pressures on their coastlines: development, conservation, recreation, and resource extraction. Its stated goal is to “preserve, protect, develop, and where possible, to restore or enhance the resources of the nation’s coastal zone.” States that participate develop their own coastal management programs, which then receive federal funding and technical support.
Environmental Pressures on Coastal States
Coastal states face a set of environmental challenges that landlocked states largely avoid. The most consequential is sea level rise. By 2050, relative to levels measured in 2000, projections show sea levels climbing 0.40 to 0.45 meters along the East Coast, 0.55 to 0.65 meters along the Gulf Coast, and 0.20 to 0.30 meters along the West Coast. The Gulf Coast faces the steepest increases, which compounds the region’s existing vulnerability to hurricanes and storm surge.
Caribbean and Hawaiian coastlines are projected to see rises of 0.20 to 0.35 meters, while northern Alaska faces about 0.30 meters of increase. Southern Alaska is a rare exception, where land is actually rising faster than the sea due to geological rebound from melting glaciers, resulting in a relative sea level decrease.
These numbers translate into real consequences: saltwater intrusion into freshwater supplies, erosion of beaches and wetlands, increased flooding during storms, and the gradual loss of low-lying land. For the 87 million Americans living in coastline counties, and for the ports, military bases, and infrastructure concentrated along the coasts, even a fraction of a meter matters.
Coastal State Responsibilities
Being a coastal state comes with obligations that inland states don’t share. On the international stage, coastal nations must allow innocent passage through their territorial seas, cooperate on fisheries management in shared waters, and protect the marine environment within their EEZ. They also bear responsibility for search and rescue operations in their maritime zones and for maintaining navigational aids like lighthouses and channel markers.
Within the U.S., coastal states that participate in federal management programs take on duties related to shoreline development permitting, wetland protection, public beach access, and hazard planning. They manage port operations, oversee commercial fishing regulations within state waters (generally the first 3 nautical miles from shore), and coordinate with federal agencies on everything from oil spill response to marine sanctuary management. The combination of economic opportunity and environmental stewardship makes coastal governance one of the more complex roles any state or nation takes on.