Yes, but the problem then is that you would always have to carry at least a pair of goggles so you can see under water, especially if there is a lot of salt in the water. And if you can't make the change within the time you can hold your breath, you would also want to have a snorkel with you.Or you can simply change lenses under water. No dust.
Every time you focus or zoom, you move elements. Moving elements have to displace air to move. Air has dust in it, even if you're in the best clean room in the world. So focusing and zooming will always move dust in and out of the lens. If it's attached to the camera, some of it will get into the camera.That's a thought. Although depending on the configuration of the lens elements having dust enter the lens doesn't necessarily mean it will make its way into the camera.