Can ducks swim under the water.
or are they like buoys and can only float?
Depends on the type of duck! Some are divers (going from the air to under water to catch food), others just feed on the surface sticking their heads under. Their are far less diving breeds (they eat fish) than the others that eat grasses and grains.
No they only stick their heads in the water to grab some food.
They can swim and fly
It is possible for a duck to swim under water. However, only all do as some of them are surface peddlers and they use their paddling feet to float gently beneath and propel.
The world may never know...
I believe they are surface swimmers, or like what you say, buoys.
Nope, but they can stick their heads underwater to grab food, making their butts stick up!! lol :)~Lexi ;)