EDIT: It looks like the spawning of the pools may have been nerfed... They're far less frequent than they were last night and only appear to spawn on the lower few tiers. Possibly I was just unlucky; I'll post back after hanging out there for a half hour or so. [So it would appear... I only encountered five pools over the space of 45 minutes.]
From what I've seen so far, this will only net you Mountain Trout, but anyway:
Schools of mountain trout actually spawn in Azshara, on the pools of the massive waterfall on the northern cliff face bordering Hyjal. It should be noted that you need some method of flying (fly hack, spirit gryphon, rocket helmet, etc.) to get up there.
Coords are in the bar in the top left corner of the screenshot if you need them.
As you can see, you can get several schools in a pool. The most I encountered was five at once on the pool fourth from the ground.
I saw no mention of this through search, but it's certainly possible that I missed it. If it's been found, let me know. xP