Editors' Summary: In the landmark Mono Lake case, National Audubon Society v. Superior Court, 13 ELR 20272, the California Supreme Court ruled that long-established water rights are subject to limitations protecting the public trust in navigable waters. The decision is introduced in Rossmann, The Public Trust in Appropriated Waters: California High Court Decides Mono Lake Case, 13 ELR 10109 (1983). In this Article, Harrison C. Dunning analyzes the implications of the decision. Professor Dunning explains that the ruling is a logical extension of the application of public trust protection in land law. It also is a significant change in California water law because it establishes that the state water board has the duty both to consider public trust values in approving and reviewing water allocations and to minimize harm to those values to the maximum extent feasible. In addition, the case is significant because the court seemed to treat the public trust as an expression of the authority of the sovereign over "common heritage" resources. Professor Dunning assesses the accommodation of the Mono Lake decision with existing California water law and analyzes its likely application to groundwater management and federal water rights. He also suggests that the court's reluctant affirmation of dual court and water board jurisdiction over water resource public trust cases was intended to allow judicial usurpation of water board jurisdiction only to the extent necessary to ensure that the board properly exercised its newly articulated responsibility to protect public trust values. He concludes by noting that the decision should be viewed not as a disruption of a stable body of law, but simply as the most recent in a series of adaptations of California water law to keep it in step with contemporary needs for water resources.