Mo. Rev. Stat. § 236.230
Every person who shall erect or maintain, or cause to be erected or maintained, in or across any of the waters of this state, unless said waters be wholly upon his own premises, any dam or other obstruction, no matter for what purpose, and shall not place and maintain thereon an apron or chute not less than fifteen feet wide, and sloping from each side to the center, so that the center shall be at least six inches lower than either edge, and having an inclination of not more than forty-five degrees, and so situated that the main current of water, impeded in its natural flow by the dam or other obstruction, shall pass over the same, or who shall not so construct or arrange such dam or other obstruction that it shall be lowest at the point where the apron or chute shall be placed, and low enough for the free passage of fish over the same each way, whenever the stream in which the same shall be situate shall be swollen beyond its ordinary size, shall be guilty of a misdemeanor, and shall be held to be guilty of a distinct offense each day he shall be in default as aforesaid; and every dam or other obstruction erected or maintained in violation of this section, shall be a public nuisance, and may be abated as such.
§ 236.230, RSMo