What are USCG Inland Waters?

Inland Waters are U.S. waters shoreward of Boundary Lines. Exceptions exist, like a 12-mile corridor in the Gulf of Mexico. MM-SEAS helps.

2 mins read・Sep 16, 2022
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Inland Waters are defined as the navigable waters of the United States shoreward of the Boundary Lines, and excluding the Great Lakes.

Nautical chart with markers.

What is the Boundary Line?

The Boundary Line generally follows the high tide waterline along beaches and shores, and is extended across the entrances to small bays, inlets, harbors, rivers, the ends of breakwaters or jetties. The Boundary Line does not include the Great Lakes.

Are there Boundary Line exceptions?

Yes. Some of the most significant exceptions are:

  • In the Gulf of Mexico between the Marquesas Keys, FL, and the Rio Grande river mouth, TX, the Boundary Line is located 12 nautical miles offshore.This creates a 12-mile-wide coastwise marine corridor inside of which non-load line vessels may operate. For ease of navigation, this Boundary Line coincides with the "Territorial Sea" boundary marked on nautical charts of the Gulf.
  • Also in the Gulf of Mexico along the western coast of Florida, Congress widened the load line-exempted corridor to 15 NM offshore (i.e., 3 NM west of the Territorial Sea boundary shown on charts) between Crystal Bay and Hudson Creek.
  • In New England waters, the Boundary Line follows a series of lights and offshore buoys from West Quoddy Head Light (at the U.S./Canadian border) to Race Point Light (at the tip of Cape Cod). Like the Gulf of Mexico, this also creates a coastwise corridor inside of which all vessels may operate without a load line. However, unlike the GoM Boundary Line (which is a constant 12 NM from the coast), the New England Boundary Line does not follow the coastline and therefore is an irregular distance offshore.

Where is the full list of rules?

The full list of rules defining the Boundary line can be found in 46 CFR Part 7

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About the author

Nate Gilman
Nate Gilman

Nate has over 15 years of professional maritime experience and has hawsepiped his way to a 3rd Mate Unlimited Endorsement with full STCW compliance. He is proud veteran of the NOAA Commissioned Corps.

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