Hi Deb. Welcome. I've been to Belize and Cozumel many times. These are wonderful snorkeling spots. Check out www.caribbeanmag.com
. Very good site. Our family enjoys Chankanaab National Park in Cozumel. Fantastic snorkeling can be had here. It's about a 15-20 minute ride from the cruise piers. It will not disappoint. There is a fee to enter the park, but it's worth every penny. Lounge chairs, food, drinks, music, lockers, changing rooms, showers, nature trails, beautiful landscape, crystal blue waters, beautiful tropical fish. Bring your cabin towels with you.
In Belize, we snorkel at Goff's Cay. Gorgeous. Gail's Point at the Barrier Reef is another excellent snorkeling and diving spot. Belize also has a baboon sanctuary, a zoo, cave tubing (haven't done yet, but we will be doing that on our next cruise to Belize.) The cave tubing is supposed to be awesome.
Hope this helps. Let me know if you need more info. A'ndrea