This required max fishing of 300, a good fishing pole & and a good supply of the +100 lures. Somesort of water travel form is a big bonus.
There are 6 fishing spawns in the waters on eastern Azshara, Pools of Elemental Water. From these pulls you can fish Globe of Water, Elemental Waters & Essence of Water(which sell decently). As a shaman I get waterwalking, which is basicly cheating when it comes to any competition.
Here is a map of all the spawn point.
http://img144.imageshack.us/img144/8586/azsharafishsk4.jpg
This map was created from memory as the realms are down for maintainance, but that is roughly where each spawn is. They have a respawn timer of around 1 hour. If you manage to get all 6 points uncontested you can easily harvest 8 Essence of Water in under 30 minutes.