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WoW Achievements. Fishing. The Lurker Above.
"Fish up The Lurker Below in Serpentshrine Cavern."
(part of Accomplished Angler)

You need:
1) A way to walk on water (levitate, water walking, etc.)
2) A way to avoid falling damage (levitate, slow fall, bubble, blink, etc.)
3) 300 fishing skill

Group up with someone, convert to raid, enter SSC, take two elevators (no enemies), jump down (not into water, but "on it", fish in the water will crush you in seconds) and walk on water to Strange Pool, fish until you get Lurker up and achievement. (Then you'll most likely visit Spirit Guide, so do this without any gear). Run back to instance if you have gear in inventory.

Credit go to Spleen and Gihelle @ El's Extreme Anglin' Forums (and of course El for THE best WoW fishing site).

for more info on fishing achievements, check El's Extreme Anglin':
http://www.elsanglin.com/achievements.html

p.s. The boss is "Lurker Below". Achievement is "The Lurker Above". As I show, these are easily mixed up :) (less info)