Hi shamrock,
I don't know of an actual snorkeling excursion for Roatan, but I was on Roatan last October on my Legend Cruise and if you go to Tabayana Beach you can snorkel the reef right from the beach and it's gorgeous!!!! We just caught a taxi over to the beach ourselves and it was fabulous. One of the best places I've ever been. The reef is beautiful with bright blue and yellow fish, it's like looking in an aquarium only better!! We rented a sea kayak and paddled out to the reef (it's a very short paddle) and snorkeled off the kayak. Enjoy your cruise!
Happy Sailing!!


Future Cruises:
Carnival Destiny - October 2009
Carnival Dream - September 2010
Past Cruises:
Carnival Imagination - September 2008
Carnival Legend - October 2007
Carnival Imagination - January 2007
Carnival Imagination - September 2006
Carnival Fascination - May 2005
Carnival Imagination - November 2004
Holland America Zuiderdam - May 2003