Is ONE PIECE episode 620 filler?
Canon No, episode 620 of ONE PIECE is canon.
#620
A Critical Situation! Punk Hazard Explodes!
絶体絶命！パンクハザード大爆発
Aired 10 Nov 2013
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.