All female swimmers were called Bikini Ladies in the Japanese versions.
In the international releases of Diamond and Pearl, Platinum and HeartGold and SoulSilver, male swimmers had their speedos, which is only present in the Japanese version, replaced with swim-trunks.
In the Japanese version of Gold and Silver, female swimmers were winking at the player.
In Black and White, a female swimmer asked, "Are you here to see Cynthia in a swim- suit?"
It's also possibility, that the male swimmer is actually based for similar looking character from 1989 Nintendo Entertainment System game Mendel Palace /Quinty, which was also developed by Game Freak, Inc.