The surf's up position is done in the water on a surf board. It can only be done when the waters are calm. To get into this position, the receiving partner lies face down and flat on the surf board. Then, the partner climbs on top and enters from behind with their chest against their back and arms on their arms.
More About The Surf's Up Position
This position is challenging because the surf board must not be moved enough to tip it over completely. The position is most easily approached by beginning in waist deep water. This allows the partners to get into position more easily than in deep water. The nature of the position adds an element of excitement, as it means semi-public sex.