Complete a new collection to unlock the Skimming the Depths mastery, and speed through Tyria's abyssal depths with ease. The submersible Skimmers will be available to owners of Guild Wars 2: Path of Fire beginning on August 25, by unlocking and training a new "Skimming the Depths" mastery. Ahead of that, a week-long World vs World bonus event will kick off on August 14 with a 25 percent bonus to reward-track progress, double experience points, and a 50 percent bonus to magic find.
https://www.pcgamer.com/guild-wars-2s-skimmer-mounts-are-going-underwater/