Abstract: The invention relates to a water craft with a preferably closed buoyancy body (1), a propulsion motor (2), arranged within the buoyancy body and a propulsion fin (14), driven by the propulsion motor, designed to generate drive by means of a reciprocating movement. An efficient close to natural movement of the water craft is possible, wherein the propulsion fin (14) comprises an elastic retainer body (6), fixed to the buoyancy body (1) at a joint and an attachment point is provided at a given distance from the joint (16) which is engaged by an operating mechanism to exert a torque on the retainer body (6).