Click here for the map
In patch 1.9, Blizz added special fishing pools, or as I sometimes call them, swirls, that contain specific items. They vary some, depending on the zone. There is a very good thread on the WoW forums that details some of the things available and the locations, thanks to Pleather on the Stormreaver server for collecting the information. These pools include the new Sagefish and Greater Sagefish, as well as Firefin Snapper, Oily Blackmouth, Deviate Fish, and floating debris piles where you can get (unlocked) trunks that contain crafting materials and equipment.
Also, in one zone, Azshara, there are swirls called 'Patch of Elemental Water', where you can fish up elemental water items: Globe of Water, Elemental Water, and Essence of Water. Located mostly in the Bay of Storms there, these are arguably the highest level, and most profitable, fishing spots in the game. I've spent some time collecting data on the locations of these pools, and this page is dedicated to detailing this information.
First, in order to fish in the Bay of Storms, you need a ridiculous level of fishing skill. A total of 420 is needed to guarantee landing what you catch, though you can make the attempt to fish with as low as 350 (I believe), though you will rarely land a fish with that skill level. Use lures and equipment to raise your skill if needed. The best fishing items can be gotten at the Stranglethorn Fishing Extravaganza contest, so you may want to try that...with the items there, you can get your skill to 350, there is a +2 enchant for gloves, and lures give up to 100 bonus as well. In my observation, if you can get your skill to 420 with some combination of the above, you won't miss many fish at all. I regularly fish at 415, and only miss a very few.
The pools that contain the elemental items (called a 'Patch of Elemental Water') are spread through the zone in the coastal area known as the Bay of Storms. The area is patrolled by mid-50 level elite giants (as well as a few other mobs), but they're mostly easily avoided if you aren't too low a level. These pools are in set locations around the bay, and it appears that only one (at most) pool is active at a time. There are possibly 7 locations we've discovered, and the locations are shown on the map I've made (full size map)
Notes:
Location 1 is slightly outside the 'Bay of Storms' itself, and requires a lower fishing level
Location 2 is at Hetaera's Clutch
Location 3 is at Scalebeard's cave
Locations 4-6 will probably be renumbered when/if the 'unverified' spot is verified (by me anyway)
I'll include more information as it comes up, and feel free to contact me if you want to contribute to the cause...I can be reached in-game (Thalenia on Uther), or drop me a note at thalen (at) earthlink.net.
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Here's a couple pictures of what the swirls in Azshara look like...one from above, one from below (the latter is from about as far away as the swirl would show up, just to give you an idea at what range you could see them...subject to your graphics settings of course)
Also, in that same area is something called a 'swirling maelstrom' - part of a quest line somewhere, here are a couple links to what that looks like.
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Thanks for help on this information:
Pleather of Stormreaver for the information on the new fishing nodes in general
To my guild, Shinra Inc, for putting up with my fishing tales, as if anyone could care less about my exploits ;-)
And thanks sincerely to Andarie (of Shinra Inc) for sporadically being online & frequently walking away from the computer. I couldn't have done it without her ;-)
Also, thanks to all the *%&@ elite giants in there for leaving me alone while I figured all this out...
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Lastly, if you're on Uther, and you are in the Bay of Storms following this guide or generally hanging around, and you see this ugly fish swim up...it's just me showing off my trinket from the fishing contest (plus it give me better swim speed and underwater breathing), so don't be alarmed, and say 'Hi' if you speak common (or just wave if you don't) ;-)