By the law of nature these things are common to mankind – the air, running water, the sea, and consequently the shores of the sea. —Emperor Justinian, 530 AD

The Public Trust Doctrine obligates government to protect and preserve waterways for public uses. As opposed to one single law or policy, the public trust doctrine is a guiding principle of government, composed of a body of laws and legal precedents. The public trust doctrine asserts that the state holds water ways “in trust” for use by the public. These public uses typically include navigation, recreation, fishing, but in California, have been expanded to include ecological values. As the trustee for the citizens, the state is obligated by the doctrine to protect rivers and wetlands for use by the public.

To better understand what the doctrine obligates the state to do and what implementation of the doctrine looks like, we must understand the doctrine’s history and examine the role the public trust doctrine played in its most prominent case, the Mono Lake decision


mono-218251_960_720In the 6th century, Byzantine emperor Justinian first invoked the public trust doctrine to make sure no single group or interest monopolized the waterways. Access disputes between fishermen, merchants and sailors made it necessary for Emperor Justinian to take a stand on the issue. His proclamation that no one could own the waterways, that they were “common to mankind” has reverberated to this very day.

Since then, the doctrine has evolved to provide stronger environmental protection. The law was incorporated into English Common Law, and passed down to the US through prominent court cases at the Federal (Illinois Central) and California state level. Justinian’s version of the public trust doctrine ensured that the public had access to water and tide resources, and protected the resources from encroachment by private enterprise. However, in the 1970s, the doctrine was used by environmental advocates for protection of environmental resources in litigation, which expanded the scope of the public trust doctrine. The best-known example is the Mono Lake decision.


The California supreme court’s decision in 1983 illustrated the true power of the public trust doctrine—to obligate the state to protect and maintain the ecological values of a water body.

In 1979, the Mono Lake Committee (MLC) brought suit against the Los Angeles Department of Water and Power (DWP) for violating the public trust doctrine in its diversion of water from the streams feeding into Mono Lake.  DWP Diversions caused the lake level to recede to ecologically dangerous levels, threatening alkali flies, bird populations, and tufa structures. The MLC argued that the state was obligated to protect them because “the shores, bed and waters of Mono Lake are protected by a public trust.”

In 1983, the court issued a decisive ruling in National Audubon Society v. Superior Court that clarified the role of the public trust doctrine in California water law. The State Water Resources Control Board followed up with its own water rights decision to implement the court’s will. Though the decision essentially obligated DWP to reduce diversions to a level that would protect public trust resources, the court’s decision did not place the public trust doctrine above other water laws in California. Instead, the courts decided that the state should “attempt, so far as feasible, to avoid or minimize any harm to those [public trust] interests”.


The Public Trust Doctrine plays a vital role protecting water ecosystems, past and present. The current lawsuit by the California Water Impact Network and its partners is the front line in the legal battle to save the Delta, and the courts may reach a more final verdict on the strength of the doctrine.

Stanford University and the Public Trust Doctrine

Stanford University Publication copy


  • The California State Lands Commission does a great job explaining the public trust as it relates to land.
  • Berkeley Law’s Symposium “Joseph Sax and the Public Trust” is the best resource for scholarly articles on the public trust, including Joseph Sax’s famous article asserting that the doctrine could be used for environmental protection. The citation for it is: Joseph L. Sax. “The Public Trust Doctrine in Natural Resource Law: Effective Judicial Intervention” Michigan Law Review68.January (1970): 471.
  • Jan S. Stevens’ article for the California Water Plan Update in 2005, Applying the Public Trust Doctrine to River Protection 
  • The National Oceanic and Atmospheric Administration has a good, in-depth tutorial on the public trust doctrine.