I would say there is no depth limit, just different equipment that makes it more efficent at deeper depths. Stardard fly style reels work great up to 10-12 ft., any deeper and the 1:1 retrieve ratio becomes a handycap. Deeper than 10 I would go with a multiplier reel, 3 big ones this year are the black betty 6061, frabill 261, and the eagle claw. Another nice feature of those 3 reels is push button free spool to let line out which gets the jig back to the fish alot faster that pulling line by hand. Another thing to consider is switching to a braided line instead of mono or flouro to maintain sensativity and hooksetting power in deeper water.