Purchase 99 Midge Baskets (Swiftperch NPC), and travel to The South Shroud. This is an EXTREMELY dangerous area for your current level, so try to put your Stealth action to good use. Your target area is a small Freshwater area just south of "The Thousand Maws of Toto-Rak" Dungeon. Using the Midge Baskets, cast from the small ledge on the east corner of that little pool area you'll come across. Aggroing mobs never go there, so you can fish in peace. You will be catching 2 different kinds of fish - Nettle Stonefish and River Sphinx. Both are level 20 fish, and because this is a Fishing Hole, it nets you bonus exp, which stacks with the 300% (or 303%) that you receive when catching HQ versions. The exp is amazing!
((Added: It is also easy to obtain level 20 simply by fishing at the Fishing Hole from the previous quest at The Brewer's Beacon. The EXP there is also good. ))
Edited, Sep 4th 2013 2:08am by Swiftskye
I'm L.15 and I tried that fishing hole in South Shroud, but it says that I only sense something around. Is there a level pre-req that you might have forgotten?