Like leaves float on the water

 
 

On many smaller lakes or ponds we see the large leaves of the sea and pond roses. They always swim on the surface of the water and even in a storm they do not capsize or sink. In the tropics there are even plants with floating leaves so large that they can carry small children.
The trick with these plants is that they trap large amounts of air in their leaves. Their leaf tissue is loose and spongy, so that the cells are surrounded by a lot of air. The outside of the leaves is thickly covered with wax, they form a waterproof surface.

Water lilies © dpa
 
 

Plants that live at the bottom of water also work with buoyancy: bladderwrack and knotwrack, for example, have small swim bladders on their leaves. These are filled with air and ensure that the leaves stand straight up and do not hang limply.

Bladderwrack © Mike Guiry - www.seaweed.ie
 
 

Why can ducks swim?

 

Ducks, swans and seagulls swim on the water by paddling with their feet. But even if they are not in motion, they do not go under.
They rub their plumage with their own body fat, which makes it water-repellent. They trap large amounts of air under their fluffed feathers. The volume of the whole bird increases, but the weight hardly increases.
Thus the animal swims - body, plumage and the enclosed air together are lighter than water.

Mallards © dpa