servitude, benefiting the federal government for the purpose of regulating commerce on navigable bodies of water. The reasonable use of the water by a riparian owner is subject to the downstream riparian owners "riparian right" to receive waters undiminished in flow and quality. Federal environmental regulation of non-navigable waters under the Clean Water Act of 1972 is possible, because all surface waters eventually flow to the public ocean. This has been the subject of political controversy, for example over implementation of the Clean Water Rule. States' involvement Federal courts have long recognized that state laws establish the extent of the riparian and public right. In the case of navigable waters, title goes to the average low water mark. The Pennsylvania Supreme Court defined it as the "ordinary low water mark, unaffected by drought; that is, the height of the water at ordinary stages." Land below the low water mark on navigable rivers belongs to the state government in the case of the 13 original states. Lands between the high and low water marks on navigable rivers are subject to the police powers of the states. In the case of the original 13 states, upon ratification of the US Constitution, title to these submerged lands remained vested in the several states similar to the public or common roads. As new lands were acquired by the United States, either by purchase or treaty, title to the highways and the beds of all navigable, or tidal, water bodies became vested in the United States unless they had been validly conveyed into private ownership by the former sovereign. During the territorial period, the United States held these title "in trust" for the benefit of the future states that would be carved out of the territory. Each of the states were to come into the Union on an "equal footing" with the original 13 states. Under the equal footing doctrine, territorial states are vested with the same sovereign title rights to navigable submerged lands as the original 13 states. However, during the territorial period, the United States could convey certain of these lands under the limited circumstances of promoting commerce. Ownership of lands submerged by navigable waters was resolved by Congress passing the Submerged Lands Act, which confirmed state title to the beds of all tidal and navigable bodies of water. While the act conveyed land title to the states, non-navigable stream beds remained treated