Penguins spend their maximum of life in the ocean. Even though they are flightless marine birds; they are efficient swimmers. Penguins swim with the help of their flippers which acts as also wings in the water. The waterproof feathers protect the penguins from the harsh cold and keep them out of wet.
The other main contribution to swimming is their body structure; the streamlined torpedo-shaped body aids them to swim precisely and smoothly.
The way penguins swim in water is almost similar to that they fly in the water. While waddling on land, penguins appear to be funny and clumsy; whereas, in water penguins swim fast spectacularly with a lot of grace.