Is ONE PIECE episode 206 filler?
Filler Yes, episode 206 of ONE PIECE is filler.
#206
Farewell, Marine Fortress! The Last Battle for Escape!
さらば海軍要塞！脱出への最後の攻防
Aired 10 Oct 2004
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.