Are Whitewater Kayaks Stable?

They are the most common form of kayak hull because they are the most stable, and surf waves incredibly well.

Can you use a whitewater kayak on flat water?

On flat water you can just keep the boat flat all the time, but on white water you need to be able to edge, or lean your kayak. You need to be able to keep control of it when it's starting to tip, because that helps you to be stable in currents.

Which kayak is most stable?

If all other dimensions are equal, a sit-inside (open-cockpit) kayak is more stable than a sit-on-top kayak. In an open-cockpit kayak you're sitting lower in the boat. Your center of gravity (aka rear-end) is at or near the level of the water.