Wow, is it ever obvious you're not from here.

South Florida has the only living barrier reef in the continental United
States.  To say that there is a park with a reef is a bit like saying that
the redwood forest has a tree.  8^)

You'll have to do your own research on the dive boats in Miami.  I dive from
my own boat in Broward (Ft. Lauderdale) and Miami Dade (Miami) Counties.
There are several reefs, but in Miami, the wrecks are a bigger attraction,
as they are in Broward County.  Further north, in Palm Beach County, there's
good drift diving over reasonably healthy reefs.  We like Deeper or
Splashdown out of the Sea Mist marina in Boynton Beach.

Just south of Miami, there's a park that's probably the one you've heard of.
It's called Biscayne National Park.  It's the lesser known of Florida's
underwater parks only because it lies between Miami and the Keys, both major
dive destinations.  There's only one boat that leaves from the park (I
think), but there's more than one that dives the same areas.  If you're
looking for pretty but shallow diving, you may find Biscayne National Park
interesting.

A bit further south, about 45 minutes further, you enter the Florida Keys.
Key Largo is the northern most of the Keys and the jump off point for
Pennekamp State park and the Key Largo Marine Sanctuary.  This is Florida's
best known underwater park and where you'll find the Christ Statute and
other "touristy" attractions.  Diving ranges from shallow and bright to deep
and not so bright.  There's a few very nice wrecks in the area.  The only
operator I used regularly recently closed up and went into the restaurant
business.  Others will point you to their current favorites.

Lee