An apparatus for adjusting a human propelled watercraft having a pair of flexible fins extending into the water. The invention allows the user to easily adjust the propulsion device to match the user's leg length. The invention consists of a push button mechanism that converts a vertical motion into a horizontal motion allowing a locking pin to retract and the propulsion device to be adjusted. Once an adjustment position is selected, the user releases the button and a spring reverses the motion of the pin, locking the mechanism into position.