A paddleboard (10) comprising a right board (12) slidingly connected to a left board (14). At least one interlocking sliding element is connected to the right board 12, and at least one interlocking sliding element is connected to the left board 14. Right board (12) and left board (14) are slidable longitudinally with respect to one another only within the plane of paddleboard (10), and parallel to the long axis of paddleboard (10). Utilizing a user's legs and feet to slide right board (12) and left board (14) longitudinally causes a propulsion system to propel paddleboard (10) over the water. A suitable propulsion system comprises pivoting paddles (16) or flaps (40) mounted under right board (12) and under left board (14).