Level up your artifact fishing pole without waterwalkingIt's a little bit harder without waterwalking, but a very good spot is when the World Quest Into The Whirlpool is active. This lets you use a portal at 30.6 62.0 in Val'sharah to get into a closed underwater cave. The quest needs you to catch fish in here, but it is also very nice for farming rare fish to level up your pole.
There are always 10 pools of fish active in the cave, and every time you finish one, a new one appear, so there's always lots of pools available. Just fish in these, and you get plenty of rare fish as well as bait! The pools keep spawning even after you complete and turn in the quest, and the portal is still open as well. The only downside to this is that there spawns a few murlocs in the cave, so you need to kill these every now and then. However, they are very fragile, so it does not take long to clear them.
Level up your artifact fishing pole with waterwalkingOnce you have a source of waterwalking, leveling up your artifact fishing pole is even easier and faster. A very good spot is to farm the Ghostly Queenfish just outside of the academy in Azsuna. You will get a guaranteed rare fish on every catch, which means 50 Artifact Power per cast! You also get bait by fishing there, so this is a really good spot.
There are no mobs around this area, so just chill back and relax while you do the fishing.