Hi solosal,
I checked out the western site on Tern Lake back in June and I found it to be a fairly nice spot when it was warm and sunny. It's quite shallow for a ways in, and since the water levels are down, there's a bit more dry land leading to the water's edge. There's a also a rock point near the camp site that may be a nice place to hang out and perhaps cook meals (again, more accessible now due to the shallow conditions). I'm not sure how conducive to swimming the lake is. I haven't been by Loft Lake for a couple of years, but I stopped at the site closer to the trail which is a bit elevated from the lake with good water access. The other site (the northern one I think?) is by a sandy beach area and from what I understand is a great place to swim.
Hope this helps, and have a great trip!
Rich