N.H. Rev. Stat. Ann. § 498:6

Any legal right, public or private, infringed by a change in the water level of a natural lake or pond, or by the casting or dropping into a watercourse of sawdust or other waste of a saw or lumber mill or any other material, and the water rights of riparian proprietors on a stream may be ascertained and enforced in a constitutional manner on a bill in equity without prior ascertainment of the right by an action at law; and rights of boating, fishing and navigation may be enforced on a bill in equity brought by the attorney general in the name of the state.