Marine Conservation Agreements
A Practitioner's Toolkit

Question: How are boundaries determined in marine waters?

Answer: Boundaries in marine waters are determined by international treaties and conventions, federal and state laws, and specific parcel descriptions in ownership records.

Boundaries associated with proprietary rights, user rights, and regulatory management of coastal and ocean areas can be extremely complicated, but none-the-less necessary for proponents of Marine Conservation Agreements (MCAs) to determine. Oftentimes, boundaries of regulatory jurisdictions overlap with one another and more often than not boundaries associated with proprietary rights are ill-defined or completely unknown in the water. Below is a summary of boundary determination issues for the United States. Marine boundaries for areas outside the U.S. may be addressed in one or more of the Country Analyses.

U.S. State and Federal Boundaries

An extensive primer on Shore and Sea Boundaries for the United States is available from the National Oceanic and Atmospheric Administration (NOAA). NOAA has also developed a summary manual for Marine Managed Areas: Best Practices for Boundary Making. The manual identifies many of the boundary issues that organizations may come across when working offshore. An annotated version of the manual's Appendix B (click on thumbnail text image at right) explains terms and boundaries associated with submerged lands, territorial seas, contiguous zone, and exclusive economic zone.

For a graphic depiction of offshore boundaries in the United States, click on the top thumbnail illustration at right.

A general depiction of state submerged lands boundaries can be viewed by clicking on the bottom thumbnail illustration at right.

Individual state and federal boundaries within ocean and coastal waters have several variables and consistent points that can be helpful to understand when undertaking MCA projects:

  • Terms and boundaries associated with state-owned intertidal and subtidal lands are state-specific (see United States Analyses and Submerged Lands).
  • All states' seaward boundaries generally end at three nautical miles except for Texas and West Florida, which end at nine nautical miles in the Gulf of Mexico.
  • Regulatory boundaries for coastal zone management, provided by NOAA, are state-specific (download .pdf, 29k).
  • The U.S. Federal Exclusive Economic Zone generally starts at the seaward boundary of state jurisdiction (three nautical miles except for Texas and West Florida) and extends 200 miles offshore from the baseline (state-defined and measured low water mark).
  • International waters and the open seas generally begin at 200 miles offshore, but this does not mean that countries do not exert some management and control past the 200-mile line.

Private Property Boundaries

Similar to state and federal boundaries, several variables complicate determining where private property boundaries are located within and along ocean and coastal waters of the United States:

  • The seaward boundary of privately owned upland parcels lying along the ocean coast can vary greatly—the boundaries may extend out to the high water line, the low water line, somewhere in between the high and low water lines, or somewhere below the low water line. In yet other situations, the upland parcel’s seaward boundary may be defined by the engineered boundaries shown on recorded survey plats, without regard to any tidal datum.
  • The exact nomenclature and measurement of the high water line and low water line is state-specific.
  • How far private property extends seaward is deed-specific and state-specific.
  • The private and public rights associated with private property (lying seaward of the high water line) are state-specific. Public rights on state-owned and privately-owned submerged lands are normally related to state-specific interpretations and applications of the public trust doctrine.
  • Whether and to what degree private property rights extend seaward past the fee-simple ownership boundary of private parcels, into state-owned intertidal or subtidal lands, is state-dependent.
  • Whether intertidal lands, lying between the state-defined and measured high and low water lines, can be privately owned is state-specific. If intertidal lands can be privately-owned, these parcels may or may not be owned independently of the adjacent upland property. The adjacent upland property and the intertidal property may have been severed (if once part of the same parcel) or may have been established originally as separate parcels.


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