This is one of those quests that can easily be missed if you aren't looking for the mobs in the right area. In fact, unless you run the Alliance version, where it is far harder to actually miss out on said quest, you might not know this one exists.
If you've done the Alliance quest and are looking for the equivalent Horde-side, you might not be at the right altitude. Keep heading down if you can't find any of the quest mobs. You'll likely find some very close to Underlight Canyon.
Just remember that if you're going to use a /target macro to hunt for the targets that it will detect them quite a few "levels" above where they typically are. If you're still seeing thick forests of kelp, you're not far enough down.
The mobs themselves are easy. They can poison and use an immobilizing/"stun" move that does damage called "Strangle Rope", but the damage it does is negligible by this point.