The most direct route for that specific niche is definitely specialized story sites, but it depends what flavor you're after. Straight-up erotica with that setting? Try sites like Literotica or ASSTR—use their search or category tags, 'pool' or 'summer' usually pulls up a bunch. The quality's a total mixed bag, from surprisingly well-paced tension to just... mechanical. Sometimes the buildup around the party atmosphere—wet clothes, whispers over chlorine smell, the risk of getting caught—is better than the explicit parts.
If you want more plot wrapped around the steam, some romance novelists write pool/beach club scenes into longer books. I stumbled into one last summer, 'The Summer Retreat,' where a whole chapter was this incredibly drawn-out midnight pool encounter during a fancy resort party. It worked because the characters had been circling each other for 200 pages. E-book stores with strong romance categories and searchable keywords ('pool party,' 'summer fling') can unearth those. Audiobook versions of those scenes add a whole other layer, depending on the narrator's delivery.
Honestly, I sometimes just search a phrase like 'poolside confession' or 'chlorine kiss' on Goodreads lists or even Twitter threads—readers love sharing where they found specific tropes. It's a bit of a dig, but finding that perfect blend of setting and heat feels like a win.