S.D. Codified Laws § 42-8-44.1
Any diver using a self-contained underwater breathing apparatus, a forced air breathing line system, a snorkel, or any other means of underwater air supply for the purpose of underwater activity, operating in the waters of this state, except in an area from which all motorboats or sailboats are prohibited from operating, shall perform the activity within an imaginary cylinder extending downward from an imaginary circle formed on the surface of the body of water by revolving a seventy-five foot radius three hundred sixty degrees about a point marked by the display of a flag as provided by this section. The flag is referred to as the diver-down flag. The diver-down flag shall be a rectangle with a bright red field crossed by a diagonal white strip running from the upper-left corner to the bottom-right corner of the rectangle and shall be clearly visible and securely attached or anchored to a float, a rubber tube, a diver, or a boat. A violation of this section is a Class 2 misdemeanor.
SDCL 42-8-44.1