Snorkeling is a great activity to enjoy while in Key West. The water around the the Florida Keys is very clear and makes fish and coral viewing easy to enjoy. You have a variety of options to do this. Use you own equipment or rent the gear you need. One piece of equipment I used was a an air chest vest that will assist you to float a little easier and not to swim as hard. You will find many tours and guides available to meet your needs for a few hours to all day adventures. In Key West you can go over to Fort Zachary Taylor State Park and find equipment rentals on the beach. I enjoyed this one afternoon and was able to view many types of fish around the rocks at the beach. While I was there, a group of people went out past the rocks and saw barracuda and a manatee swim by. With just a swim goggle on I was able to see many small tropical fish in just 1 – 2 feet of water along the shore line just like the ones in your aquarium at home. The kids would get a kick out of this.
The Dry Tortugas National Park Ferry tour, offers as part of the tour package is snorkeling equipment to use. There are a couple of beaches around the island to snorkel from. I enjoyed a swim around the old dock pilings to view many types of fish and coral. A couple of photos I took from my swim are below. I used a disposable underwater camera I bought on the ferry boat to take these photos.
As you see the swimmer in the background, you are not in deep water as their head looks to be out or near the water line.
Overall, you have to try snorkeling and take advantage of viewing the beauty the coral reefs have to offer. (PS, while I was snorkeling each time, my wife enjoyed the beach sunning, as she is not a water person. Again you both are at at the beach enjoying what you want to do.)