I was out that way for a week last summer. We stayed at a campground south of penticton and spent the week on Skaha lake (lake on south end of Penticton). It's the only lake we hit when we were down there but it was awesome. Water was warm. The south bay of the lake was glass all week (five days in a row) Very low traffic all week at the south bay as well. There was a course at both ends of the lake for the skiers out there. Also some wicked cliff jumps (also in the south bay on the east side) when we needed a break from skiing.
I will be heading back. It is not that far from Osoyoos.