For this quest, I took the boat as outlined in the quest. I’m standing in front of the NPC (Rokor), and it isn’t giving me the option to turn the quest in. I’ve walked around and over him a few times. Tried restarting the game, computer, waiting a day, dropping the quest and picking it back up…no luck.
Update: had to swim across the channel before it took. 
this quest was bugged for me today as well. I was able to abandon it, and then Rokor had the next 2 quests available anyway. took the boat 3 times before giving up though… annoying.
Thank you! For whatever reason just swimming across that little bit of water and coming back triggers it.
Damn, this is still bugged, swimming didn’t help me at all either. C’mon blizz, help a seeka out <3
Thanks for coming back and updating. That little bit solved the issue for me.
As of May 2020 this is still bugged…
Same issue. Took the boat twice. I am sitting in front of Rokor waiting on a Blizz ticket. This is still an issue from 2019. Really?
Still an issue, July 2020. I tried swimming, abandoning the quest and trying it a couple times, etc. Nada.
Still an issue Sept 14th, 2020. Abandoned it in front of Rokor and was able to get the next 2 quests.
yea just happened to me too. 
I swam to 81.46, 44.81 and the quest triggered complete and he got the yellow question mark. Hope this helps.
Jan 2021 and this is still bugged. Dropping quest in front of Rokor did indeed let me pick up the quests but I am surprised this is still an issue.