Dove in it twice. Once to retrieve and outboard motor at 35 ffw. I can
honestly say that was the coldest
water I have been in.

The clarity of the water is good, but the lake itself is all but sterile.
Mostly rocks and trash dropped by
"people".

The summer only thermocline at around 8 to 15 feet will take your breath
away, as you can go from
around 68 to 36 or so degree's f almost instantly.

During the summer the diving in Tahoe is OK.  The visibilty is good,
30-40 ft, but you won't see much except crawdads, rocks, and sand.
You may see some fairly large schools of minnows, but not guaranteed.

July - September, the surface water temp averages 60F with a
thermocline around 50 ft.  I find that I don't need either a hood or
gloves if I stay above the thermocline, and I use a 7 mil body suit.
If I plan on diving below the thermocline, I use the same suit but add
3 mil gloves and a 5 mil hood.

Adventure Scuba is a good dive shop located in Reno, about 45 minutes
from Lake Tahoe.  I think there might be a shop in South Shore, but I
don't know for sure.

When diving at altitude, you need to compensate for the reduced
atmospheric pressure when using the dive tables.  At Lake Tahoe, add
three feet for every ten feet in depth.  Thus, a 30 ft dive is treated
as a 39 ft dive, a 50 ft dive as a 65 ft dive, etc.  If you use a
computer, follow the manufacturers instructions regarding altitude.

Have fun, but watch out for the one arm bandits.

I visited Lake Tahoe once in my life during the '80's on my trek up
thru Calif and into Nevada.  It was late March and the snow was piled
past the first story windows of the houses, so I'm guessing it was 7
to 8 ft high, and all tall along the walkways.  I was amazed that ppl
could live like that.  LOL  I'd be interested to see what you find of
the water temp, etc.  You have more hatzpah than I do, but then again
- I hate cold water diving anymore.  Please post a trip report here if
you do this dive so that we can see what you encountered.  Best of
luck to you on this trip !!  :)