It's hard to kill a swimming bird
on the water, so much of the vitals are safely submerged, and the cripples can do that alligator snake-crawl thing with their head half underwater.
* Splashy Fish - Users avoid obstacles of a swimming bird
fish and find treasures and trophies.
When we go back to the beginnings of the word duck, we see that the historically primary meaning of the lexical category in question is 'a swimming bird of the genus Anas and kindred genera of the family Anatidae, of which species are found all over the world' (see the OED dictionary).
Note that this duck--based adjective is semantically related to the primary sense of the lexical category duck, that is 'a swimming bird of the genus Anas and kindred genera of the family Anatidae\ and its rise is clearly extralinguistically related to the observation of the characteristic movement of the bird.
"The gentoo is the fastest swimming bird
. The penguin is a mixed image, but very useful in terms of presenting material.
Some birds are swimming birds
. Some birds are flying birds.