Eggbeater Flippers

Analagous to scuba flippers, an eggbeater flipper is designed to amplify the propulsion generated by the act of treading water. While treading, the feet push the water down and back, which results in a greater bouyant force or something. Anyways, the point is you get out of the water when you push your feet down rapidly.

The flippers resemble umbrellas mounted around the shins that open and stiffen when they are pushed down, but collapse when pulled up. Thus, if you modify your eggbeater by pushing more vertically and rotating your knees less, (i.e., try to climb stairs), you should be able to push yourself up and out of the water. The fins are multilayered, with one umbrella just below the knee and another one just above the ankle. The feet fit into stirrups so that the device doesn't slide up the leg.

Because these flippers collapse, it's still possible to swim horizontally, although kicking might be awkward, and could possibly deform the flippers.

NB. An "eggbeater" style kick is used when treading water. I didn't actually mean the flippers would look like eggbeaters, but instead they were meant to enhance one's eggbeater kick. I should clarify these things beforehand.