Various North Carolina fishing statutes, rules, and proclamations apply only in the Atlantic Ocean. The Division of Marine Fisheries uses as the boundary between the Atlantic Ocean and the inside sounds a federally designated line. This line delineates "International Regulations for Preventing Collisions at Sea" (COLREGS Lines of Demarcation) which were established by the Coast Guard to designate where "International Rules of the Road" separate from "U.S. Inland Rules". Individual lines were established where practical, by physical objects like fixed aids to navigation or prominent points of land, because they are readily discernable by eye rather than by instruments. Following is the actual wording from the Code of Federal Regulations (CFR) that describes these lines for North Carolina inlets.

Sec. 80.01 General basis and purpose of demarcation lines.

(a) The regulations in this part establish the lines of demarcation delineating those waters upon which mariners shall comply with the International Regulations for Preventing Collisions at Sea, 1972 (72 COLREGS) and those water upon which mariners shall comply with the Inland Navigation Rules.
(b) The waters inside of the lines are Inland Rules waters. The waters outside the lines are COLREGS waters.
(c) Geographic coordinates expressed in terms of latitude or longitude, or both, are not intended for plotting on maps or charts whose referenced horizontal datum is the North American Datum of 1983 (NAD 83), unless such geographic coordinates are expressly labeled NAD 83. Geographic coordinates without the NAD 83 reference may be plotted on maps or charts referenced to NAD 83 only after application of the appropriate corrections that are published on the particular map or chart being used.

[CGD 82-029, 47 FR 19519, May 6, 1982, as amended by CGD 83-003, 48 FR 7442, Feb. 18, 1983; CGD 86-082, 52 FR 33810, Sept. 8, 1987]

Here are the designations for COLREGS Lines in NC Waters/Inlets