KHeart_8910
Minutes later, Angie called out with an undiscernible hint to her voice, "You could wash it off at Lake Mytilene."
"It is a tattoo, Angie, tattoos do not simply wash off."
"Not in any other lake, pond, or ocean, maybe." Robin flashed her a curious glance before he could help himself. "Lake Mytilene, though- trust me. That place is something unmatched. 'Can solve 'most any problem." She spoke lowly, sounding mystified.
---
Or: Robin visits a lake to get a tattoo removed, and get some free advice. Basically "lesbian of the pool, what is your wisdom?", the fic.