Ideally all of them but also if that is impossible my importance order would be:
1.Forgotten Grotto / Because I want to make mermaid grotto
2. Brindleton Bay / Because it has that sailor vibe and it just seems odd to not sail there?
3. Windenburg / but only if sea monster stays because I'D REALLY LIKE TO MEET IT WHILE SWIMMING
4. Granite Falls / I don't even have OR yet but if I ever get it I don't think cottage holiday is complete without swimming in lake
5. Sylvan Glade/ idk could be sorta romantic
I don't really care for oasis springs and willow creek because those don't really have swimming areas anyways
and idk about sixam it seems.... kinda creepy since the ''water'' there is odd
