Lake Mead, Nevada (Las Vegas) is the closest place So. Nevadans can get wet with Scuba gear attached to their backs. The awe inspiring reefs are not here, neither are the 1,500 varieties of marine life that other dive ocean sites seem to have. However, if you want to be a good diver when you go to these cool places, Lake Mead is the perfect practice area. Lake Mead is the largest man made lake in the western hemisphere, and second in the world. There is plenty of diving off the shore with very easy access to the scuba park and other shore sites, but to fully appreciate this body of water you're better of with some kind of watercraft to get you out to the better vis (15-20') and to the available terrain (gypsum reefs) in the middle of these grand basins. Temps range from winter surface temps of about 52 F to about 78 F in mid summer. Winter is typically a better time to dive for vis and air temperature. Summer air temps can get to 115.F+ easily. Lake Mead is very easy to find: it sits on the eastern edge of the greater Las Vegas valley. I recommend this spot to anyone jonesing to get wet, without a ocean nearby.