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The public trust doctrine is the principle that the sovereign holds in trust for public use some resources such as shoreline between the high and low tide lines, regardless of private property ownership. 
The ancient laws of the Byzantine Emperor Justinian held that the sea, the shores of the sea, the air and running water was common to everyone.  The seashore, later defined as waters affected by the ebb and flow of the tides could not be appropriated for private use and was open to all. This principle became the law in England as well. Centuries later, the Magna Carta further strengthened public rights. At the insistence of English nobles, fishing weirs which obstructed free navigation were to be removed from rivers.
These rights were further strengthened by later laws in England and subsequently became part of the common law of the United States. The Supreme Court first accepted the public trust doctrine in Martin v. Waddell’s Lessee in 1842, confirming it several decades later in Illinois Central Railroad v. Illinois, 146 U.S. 387 (1892). In the latter case the Illinois Legislature had granted an enormous portion of the Chicago harbor to the Illinois Central Railroad. A subsequent legislature sought to revoke the grant, claiming that original grant should not have been permitted in the first place. The court held that common law public trust doctrine prevented the government from alienating the public right to the lands under navigable waters (except in the case of very small portions of land which would have no effect on free access or navigation).
The public trust applies to both waters influenced by the tides and waters that are navigable in fact. The public trust also applies to the natural resources (mineral or animal) contained in the soil and water over those public trust lands.
The doctrine is most often invoked in connection with access to the seashore. In the United States, the law differs among the fifty states but in general limits the rights of ocean front property owners to exclude the public below the mean high tide line.
Massachusetts and Maine (which share a common legal heritage) recognize private property ownership to the mean low tide line—but allow public access to the seashore between the low and high tide lines for "fishing, fowling and navigation," traditional rights going back to the Colonial Ordinance of 1647.  Maine's Supreme Court in 2011 expanded the public trust doctrine by concluding fishing fowling and navigation are not an exclusive list; the court allowed the general public to cross private shoreline for scuba diving. 
The public trust doctrine also finds expression in the Great Pond law, a traditional right codified in case law and statutes in Massachusetts, Maine, and New Hampshire.  The state is said to own the land below the low water mark under great ponds (ponds over ten acres), and the public retains in effect an access easement over unimproved private property for uses such as fishing, cutting ice, and hunting. 
In Oregon, a 1967 "Beach Bill" affirmed the state's public trust doctrine, and the right of the public to have access to the seashore virtually everywhere between the low and high tide marks. In California the situation is more complicated: private landowners often try to block traditional public beach access, which can result in protracted litigation.  Freshwater use rights have also been subject to litigation in California, under the public trust doctrine. 
The doctrine has also been used to provide public access across and provide for continued public interest in those areas where land beneath tidally influenced waters has been filled. In some cases, the uses of that land have been limited (to transportation, for instance) and in others, there has been provision for public access across them.
The doctrine has been employed to assert public interest in oil resources discovered on tidally influenced lands ( Mississippi, California) and has also been used to prevent the private ownership of fish stocks and crustacean beds.
In most states in the United States, lakes and navigable-in-fact streams are maintained for drinking and recreation purposes under a public-trust doctrine.
- Prescriptive easement
- Freedom to roam
- Illinois Central Railroad Co. v. Illinois
- Juliana v. United States
- M. C. Mehta v. Kamal Nath
- National Audubon Society v. Superior Court
- Public trust
- Public good
- Public space
- Public property
- Right of way
- Sax, Joseph L. (1970). "The Public Trust Doctrine in Natural Resource Law: Effective Judicial Intervention". Michigan Law Review. The Michigan Law Review Association. 68 (3): 471–566. doi: 10.2307/1287556. JSTOR 1287556.
- Slade, David C. (2008). The Public Trust Doctrine in Motion. PTDIM, LLC. ISBN 978-0-615-24111-1.
- Velozo de Melo Bento, Lucas (November 14, 2009). "Searching for Intergenerational Green Solutions: The Relevance of the Public Trust Doctrine to Environmental Preservation". Common Law Review (11): 7–13. SSRN 1709104.
- Mary Christina Wood, Nature's Trust: Environmental Law for a New Ecological Age (2014) 
- National Working Waterfront Network (July 22, 2015). "Public Trust Doctrine". Wateraccessus.com. Retrieved July 22, 2015.
- William D. Araiza, The Public Trust Doctrine as an Interpretive Canon,p. 695. 
- Dennis W. Nixon (1 January 1994). Marine and Coastal Law: Cases and Materials. Greenwood Publishing Group. pp. 105–. ISBN 978-0-275-93763-8.
- Evan Parrott (October 1, 2011).
"Maine's Public Trust Doctrine Continues to Evolve" (PDF). Nsglc.olemiss.edu. Retrieved July 22, 2015.
[The] Maine Supreme Judicial Court affirmed . . . that the public has a right to walk across [privately owned] inter-tidal lands to reach the ocean for purposes of scuba diving.
- Emory Washburn (1873). A Treatise on the American Law of Easements and Servitudes. Little, Brown. pp. 522–.
- William Randall (November 24, 2001). "Great Ponds Act — Archive — BDN Maine archive — BDN Maine". Archive.bangordailynews.com. Retrieved August 12, 2015.
- Lee Romney (March 12, 2013). "Dispute heats up over blocked access to Northern California beach - latimes". Articles.latimes.com. Retrieved August 12, 2015.
- "Mono Lake Committee - protect, restore, educate!". www.monolake.org.
- David Bollier, "Mary Wood’s Crusade to Reinvigorate the Public Trust Doctrine", Resilience, Feb. 12, 2014.
- Michael Seth Benn, Towards Environmental Entrepreneurship: Restoring the Public Trust Doctrine in New York, 155 University of Pennsylvania Law Review 203 (2006).
- Ryan, Patrick S. (2004).
Michigan Telecommunications and Technology Law Review. 10 (2)
Application of the Public-Trust Doctrine and Principles of Natural Resource Management to Electromagnetic Spectrum. http://ssrn.com/abstract=556673 Application of the Public-Trust Doctrine and Principles of Natural Resource Management to Electromagnetic Spectrum. Check
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- James L. Huffman, "Fish Out of Water: The Public Trust Doctrine in a Constitutional Democracy " Issues in Legal Scholarship, Joseph Sax and the Public Trust (2003): Article 6.
- "Restoring The Trust: Water Resources & The Public Trust Doctrine, A Manual For Advocates" by the Center for Progressive Reform, September 2009
- Mono Lake Committee website