As an increasing number of communities in the United States face significant flooding, droughts, and degradation of water quality, interest in the management of interstate water basins has heightened. Interstate water management requires a number of interests to be balanced, including different priorities among states affected by the particular water basin, federal interests in federal water projects, and private interest groups who may be affected by regulation of the basin. Because of these competing interests, interstate water management often becomes controversial and may lead to lengthy legal disputes among the parties. The Chesapeake Bay provides one example of an interstate water basin with a long history of joint efforts to find long-term solutions to water resources problems affecting federal, state, and private interests. This report explains the legal authority of the federal and state governments to manage water resources. It also examines the role of interstate water compacts to address management issues in interstate water basins. The report analyzes efforts made to resolve disputes in the Chesapeake Bay to illustrate the concurrent roles that states and the federal government may play in managing interstate water resources. Historically, the federal government has claimed control over the nation's waterways to facilitate navigation. The states have claimed authority to control the water resources within their own boundaries. Many waterbodies cross state boundaries, though, and one state's management of part of a water basin may affect the portion of the basin located in another state. To address these competing interests, states may enter into interstate water compacts with the consent of Congress that provide uniform rules for management of the basin. The Commerce Clause of the U.S. Constitution grants the federal government broad authority over water resources within the United States, empowering Congress "to regulate Commerce ... among the several States." The U.S. Supreme Court has interpreted the Commerce Clause broadly. Under the Commerce Clause, Congress may regulate (1) channels of interstate commerce, for example, highways and rivers; (2) instrumentalities of interstate commerce; and (3) activities that substantially affect interstate commerce. The U.S. Supreme Court historically has held that the federal authority over water derives from the Commerce Clause and the significant federal interest in promoting navigation throughout the nation's waterways. Commerce includes navigation. The power to regulate commerce comprehends the control for that purpose, and to the extent necessary, of all the navigable waters of the United States which are accessible from a State other than those in which they lie. For this purpose they are the public property of the nation, and subject to all requisite legislation by Congress. This necessarily includes the power to keep them open and free from any obstruction to their navigation, interposed by the States or otherwise; to remove such obstructions when they exist; and to provide, by such sanctions as they may deem proper, against the occurrence of the evil and for the punishment of offenders. The breadth of this authority has been recognized repeatedly. In 1899, the Court explained that the states' authority over water was subject to "the superior power of the General Government to secure the uninterrupted navigability of all the navigable streams within the limits of the United States." According to the Court, states' interests in controlling waters within their boundaries could not restrict federal actions related to water. Even if the federal action would interfere "with the state's own program for water development and conservation ... [that program] must bow before the 'superior power' of Congress." The Supreme Court has held that the constitutional authority of the federal government "is as broad as the needs of commerce." It has explained that maintaining the navigability of waterways is only one of the various purposes for which the government may claim authority over water. In other words, congressional authority to regulate water resources may serve a number of purposes other than navigation, such as flood control, hydropower, and watershed development. Thus, although the federal government often defers to states' authority regarding allocation and water management, a state's authority over its waters is "subject to the power of Congress to control the waters for the purpose of commerce." The U.S. Supreme Court has long held that a state owns the navigable waters within its borders. In 1842, the Court explained that when the United States was formed, "the people of each state became themselves sovereign; and in that character hold the absolute right to all their navigable waters and the soils under them for their own common use, subject only to the rights since surrendered by the Constitution to the general government." Under the constitutional equal footing doctrine, states that later joined the union acquired the same rights granted to the original states, and therefore also acquired ownership of their state's navigable waters upon achieving statehood. It is notable that, although the Court recognized state ownership of water within state boundaries, it also indicated that the state's interest in its waters could be limited by superseding rights assigned under the Constitution to the federal government. In other words, the state may not claim absolute authority to navigable waters if the federal government has constitutional authority to act with respect to those waters. The competing interests of the federal and state governments may result in disputes over the management of water resources in interstate basins. These disputes may be addressed through interstate water compacts, which allow states to cooperate in solving problems that cross state lines. Several dozen interstate water compacts have been established over the past century, and most states have engaged in the compacting process at some point. The U.S. Constitution generally requires congressional consent for such an agreement between states, but does not specify a particular procedure for states to enter compacts. Congressional consent is necessary for a compact if it "may tend to increase and build up the political influence of the contracting States, so as to encroach upon or impair the supremacy of the United States.... " Usually, consent by Congress takes the form of a joint resolution or act of Congress, which specifies its approval of the text of the compact, adds any conditions or provisions it deems necessary, and often embodies the compact document. Generally, to form an interstate compact, states need to negotiate and agree upon the terms of the compact. Each state legislature and Congress then must enact the precise language of the agreement. As an alternative to approving the exact language of the negotiated compact, Congress may give its consent in the form of prior authorization in order to encourage agreements in a specific area. So long as the states enter into a compact that fits into the preapproved purposes enacted by Congress, the compact would be valid. If any provisions were different from, or added to, the preapproved ones, congressional approval may be required for the compact to take effect. One Congress cannot bind a future Congress, and thus, the possibility exists that Congress might amend any compact notwithstanding any prospective congressional approval. Furthermore, the Supreme Court has held that Congress retains the power to override provisions of an interstate compact through subsequent legislation. The Chesapeake Bay watershed covers 64,000 square miles and includes parts of six states (Delaware, Maryland, New York, Pennsylvania, Virginia, and West Virginia), as well as the District of Columbia (hereinafter referred to as the states or the watershed jurisdictions). It provides an example of joint federal-state efforts to address water management across jurisdictional lines. Under its constitutional authority discussed above, Congress enacted the Federal Water Pollution Control Act, which is commonly referred to as the Clean Water Act (CWA), to control pollution of the nation's waterways. Efforts to address pollution in the Chesapeake Bay illustrate the various roles that states and the federal government may play in managing water resources. In addition to Congress's enacting the CWA to create a coordinated approach to pollution control through federal statute, federal and state authorities have used other measures to manage the Bay's resources. The U.S. Environmental Protection Agency (EPA), the Chesapeake Bay states, and private regional interests have entered a number of interstate agreements in efforts to address the issues facing the watershed, as discussed below. Most recently, the Obama Administration announced new restrictions on pollution that would apply across the Chesapeake Bay states. Each of these approaches—joint authority under federal statute, interstate agreements, and federal administrative action—is addressed below. The CWA governs pollution of the nation's waterways. In the CWA, Congress identified a number of goals "to restore and maintain the chemical, physical, and biological integrity of the Nation's waters," including restricting the discharge of toxic pollutants and controlling various sources of pollution. Congress also acknowledged the role of states in pollution control, stating that "[it] is the policy of the Congress to recognize, preserve, and protect the primary responsibilities and rights of States to prevent, reduce, and eliminate pollution, to plan the development and use ... of land and water resources, and to consult with the Administrator in the exercise of his authority" under the CWA. The result often is referred to as "cooperative federalism," an arrangement in which the federal government establishes goals and national policy, and states are responsible for day-to-day implementation of the law. To achieve the statute's objectives, the CWA regulates pollution by prohibiting point-source discharges into the waters of the United States except if made in compliance with the CWA. Two of the primary enforcement mechanisms that regulate discharges into waters of the United States, including the territorial seas, are the use of permits under the National Pollutant Discharge Elimination System (NPDES) and requiring permits for dredged or fill materials discharged. Each of these approaches includes explicit recognition of the roles of both the federal government and the states in managing waterways subject to the statute. The CWA requires states to set water quality standards for waterways within its borders, which are then subject to federal approval. Water quality standards consist of the designated use of a waterbody (e.g., recreation or water supply), water quality criteria necessary to protect the designated use, and a nondegradation statement to conserve and protect existing uses. The statute also requires EPA to establish effluent limitations for point sources that identify industry-specific national standards that limit the discharge of pollutants.