Abstract: A toy is provided which simulates a marine creature. The toy comprises a body portion and a tail portion with a tail fin pivotally mounted thereto; a battery operated motor housed in a water-tight compartment in the body portion to move the tail and the tail fin relative to the body portion to propel the toy through the water; a drive to drive the tail portion comprising a pair of parallel cranks mounted opposite one another on a single spindle and driven through gearing by the motor; and a drive member extending down within the top portion of the tail, the drive member being provided with a pair of slots, each slot receiving a pin connected to one of the cranks. Buoyancy may be achieved using floats located in the body and tail portions.