Mo. Rev. Stat. § 70.340

Where a watershed located partly within any such city and partly within an adjoining state requires for the health, safety and comfort of the inhabitants of such city the construction of sewers and protection against flood, such city may, with consent of such adjoining state, but with or without the cooperation of public corporations of such adjoining state, build sanitary or storm sewers, or construct levees along the banks of, or shorten, divert or otherwise improve any natural watercourse in such watershed. Such city may, by purchase or eminent domain proceedings, acquire rights-of-way for any such sewers or improvements of watercourses.