Mo. Rev. Stat. § 252.200

It shall be unlawful for any person to place or cause to be placed or erected any seine, screen, net, weir, fish dam or other obstruction in or across any of the waters, rivers, creeks, ponds, streams, sloughs or other watercourse within the jurisdiction of this state in such a manner as will obstruct the free passage of fish up and down and through such water or watercourses. Any person violating any of the provisions of this section shall be deemed guilty of a misdemeanor and be fined upon conviction not less than ten dollars nor more than one hundred dollars and costs of prosecution.