My favorite is Lake Mead, outside of Las Vegas. More for sentimental reasons than anything else; my friends and I rent a houseboat there every summer. We spend four days basically naked in the 105 degree heat, floating in 80-degree freshwater while drinking beer and happily returning the fluids back into the ecosphere. Apologies to all of those downstream.
Runner up: Monterey Bay, towards the Santa Cruz end.
Must happen often there because I had the exact same experience when I was there 4 years ago. The outpost cabin that the inn there offers are a little expensive but Wow if you want to get away from it all it doesn’t get any better.
Kentucky lake isn’t bad either mainly because I can throw a rock from my back deck and hit it.
I’ll second that - and get a bit more specific. Bloody Bay (Negril, Jamaica). Clear, calm, warm water. You can wade out in it up to your shoulders and still see your feet. And that stretch of beach is just spectacular.
And Mrs. zoog and I are headed back there in a little over 3 weeks. Oh. Hell. Yes.