S.D. Codified Laws § 5-2-4

For the purposes of §§ 5-2-4 to 5-2-9, inclusive, the bed and channel of any lake or river in this state or bordering on this state to the middle of the main channel thereof, and all islands and sand bars lying therein shall be considered the property of the State of South Dakota unless this state or the United States has granted or conveyed an adverse legal or equitable interest therein. Nothing in said sections shall affect or impair the rights of riparian owners.