S.D. Codified Laws § 46A-10A-43
Any drainage district established under the laws of this state that has functioned in its capacity as a drainage district within three years prior to July 1, 1985 or that has assessed real property in its capacity as a drainage district within three years prior to July 1, 1985 shall be allowed to continue in that status. However, the landowners in such existing drainage district may choose by majority vote at a general election under the general election laws of this state to dissolve in order to join one or more drainage projects or drainage methods or to become or join a coordinated drainage area. Any county drainage plan shall include functioning drainage districts, vested rights described in § 46A-10A-31, the drainage plans or projects of a unit of local government and existing coordinated drainage areas formed pursuant to § 46A-10A-47.
SDCL 46A-10A-43