I think this must be the penguin. They certainly are completely flightless.
What Is The Only Bird That Can Swim But Cannot Fly?
Penguin???
Penguin
A penguin. I have a son who walks like one and they are some amazing creatures. I love it!
The only on that I can think of off the top of my head is a Pinguin. Hope that helps. MyGemmie
Penguins, true. However, a Galapagos cormorant can swim, but cannot fly. 
Further, a coot (variety of bird in the rail family, no kin to the duck) can swim but cannot fly. 
Ducks, on the other hand, can fly... And quite well, too. 
Mallard duck Other birds most likely can swim, whether they choose to ...or even need to, may be a different story. Very few animals can't swim. Most who don't either have no need to, or just don't like the water or the slick, muddy surfaces beneath the water.
