Hey all, I've been seeing lots of chat channel spam asking for locations of the new Plane of Water scavenger hunt objectives for Phase 1, so figured I'd consolidate the answers somewhere. Apologies if a guide has already been made somewhere, feel free to point it out if so.
To start, the quest to complete all 3 can be picked up in Margle Palace right near the Porticulum, at approximately [5721, 5624].
The quest NPC is located right outside of the Ghar Station at approximately [3844, 6512].
The quest requires you to find and kill Shichirin, a giant Thresher, and use 60 brisket, 30 merpho, and 30 zirthan dreamleech on his corpse. He can be found patrolling the path around Gyel Fortress.
The quest NPC can be found at approximately [6059, 6567]. I found it easiest to just use the bouncer near the Shadow Scion port and drop down onto it from above.
This quest asks you to find a hidden beach party somewhere in Draumheim. It can be found north of the Sanctum of Phydrena at [6300, 6760]. Just like most Summerfest objectives, if it is not there try sharp hopping until you find it.
The quest NPC can be found south of the Ghar Station at approximately [4210, 4525].
The objective is to find a strangely decorated hut in Tarken Glacier. The hut is located to the east of the Frystfall Trench at [5856, 2564]. Shard hop to find the hut with Christmas decorations, the quest will auto-complete when you find it.
Phase 2 (thanks Sedvick!)