Prerequisite: For this to work I believe you need to trigger the “fishing for attention” buff so you should not disable the profession appearances with specific npcs (Mahra Treebender and maybe some others).
Normal fishing of course triggers the “fishing for attention” buff and if you are using the underlight angler you will also get the “surface tension” buff and “way of the flounder” buff and if you go underwater you transform into a fish and get the fast swimming
But what to do if you are somewhere you can’t “fish”, like underwater, or on dry land or too shallow water or whatever? You open the Fishing Journal, drag the underlight angler into one of your bags, and then put the underlight angler back in the fishing journal equipment slot.
BAM you now get the buffs again!