Fathom Incher

While you're adventuring in Hallowfall you'll probably kill creatures at the Sunless Strand and find a [item=217352] which will start Gasping Plea.

Find the location marked on your map and you'll meet a [npc=219430] for the Crushing Depths storyline (Tidal Charms,Voices from the Deep,Alluring Offer) that will eventually lead to Return to the Sea with the [item=222964] reward.
/way #2215 54.52 25.33 Peculiar Fish
Make sure you're not on a mount when you are supposed to throw the fish into the water. When I did the quests, the extra action buttons for [spell=440905] and [spell=440980] didn't show until I dismounted.