The Collaborative International Dictionary
Natatorial
Natatorial \Na`ta*to"rial\, a. Inclined or adapted to swim; swimming; as, natatorial birds.
Douglas Harper's Etymology Dictionary
natatorial
1816, from natatory (adj.), from Latin natatorius, from natator "swimmer" (see natatorium) + -al.
Wiktionary
natatorial
a. Of or pertaining to swimming.