Instead of trying to compile a list of every fishable waterway, which would be one of the hardest databases to gather, consider the general level of the area that you are in but can't fish because of the level required.
If, for example, you're in a level 30-35 area and can't fish it, travel to an area that suits lvl 25-30 players and try there. Continue to work your way down until you hit the sweet spot. Well, technically, there is no sweet spot because you can fish in any waters that are at or below your level. In fact, you can fish in the starting areas up to fishing 300. The downside to fishing in the newbie zones is that you will only catch newbie fish.
By fishing in harder waters, you have the opportunity to haul in bigger and bigger fish. You won't be reeling in 30 pound lobsters from the ice hole in Kharannos.
Good fishing to ya.