I backpacked to Hart Lakes for the weekend, which I had to myself.
The water was (by my standards) fairly swimmable, and unlike last year's trip to nearby Ostrander at the same point in the year, the thermocline wasn't shallow - I didn't have cold water around my feet while treading water. This is probably because last year there was some remnant snow on Horse Ridge flowing into Ostrander, this year there were only the smallest patches of snow on the face of Horse Ridge.
As a swimming lake I prefer Ostrander - Hart has about a foot or so of soft sediment on the bottom. Deep water is reasonably quickly accessible, but I prefer not having the soft sediment.
There were plenty of mosquitoes but they mostly didn't bother me due to the breeze that started up Saturday afternoon. During calm periods I was hearing, and seeing, clouds of them, but the wind built up over the afternoon and eventually blew them away.
Pics...
Hart Lakes from the ridge above:
Clark Range, from the same point. You can see how little snow is remaining on west-facing slopes:
Morning view of the main lake:
Half Dome, Mt. Starr King, and other domes:
The pond between Ostrander and Hart. There was a small outflow of clear water from the pond.