Mo. Rev. Stat. § 241.290: Abandoned riverbeds and islands granted counties for schools.

All lands belonging to the state, not otherwise appropriated under the laws thereof, which have been formed by the recession and abandonment of their waters of the old beds of lakes and rivers in this state, or by the formation of islands in the navigable waters of the state, are hereby granted and transferred to the respective counties in which such lands are located, to be held by such counties for school purposes.