South of Marathon Key, the snorkeling at Bahia Honda State Park is ideal for beginners with it's shallow five foot deep water. There is a range of diverse marine life among the sea grass, soft corals, hard corals and tube sponges. While snorkeling, you may encounter spiny lobster, starfish, octopus, crabs, conch, urchins, trunkfish, yellow spotted stingray, parrotfish, needlefish, sergeant majors, cowfish, and nurse sharks. Bahia Honda State Park offers snorkeling off both the bay and ocean sides of the key, though the southern end of the ocean side is the best with crystal clear turquoise water. This is one of the few beach-accessed snorkeling dive sites in the Florida Keys and happens to be excellent. While there are some marked snorkeling spots on the Gulf side of the state park, by far the best snorkeling is on the ocean side. Some snorkelers report good snorkeling under the old bridge, but be aware that there are very strong currents present along with some parts falling off the bridge. Note, a diver down flag is required by state law when snorkeling at Bahia Honda State Park.
From Bahia Honda State Park, there are also charter boats heading out to Looe Key for snorkeling.
Tip - After a long day of snorkeling at Bahia Honda State Park, then grab a cool drink at Billys Stone Crab on Summerland Key or Kiki’s Sand Bar on Little Torch Key. And, if you didn't happen to spot any turtles while snorkeling off Marathon Key, you can always stop by the Turtle Hospital for a top of the hour tour of the hospital or turtles tanks located at mile post 48.5.
To reach the snorkeling in the Florida Keys by air, there are several options. The most popular option is to fly into Miami International Airport (MIA), which is served by all major US and international airlines. Also nearby, a potentially lower cost option is to fly into Ft Lauderdale airport (FLL). From either of these airports, you can rent a car to drive south on the Florida Turnpike a couple hours to reach the Florida Keys (watch out for automated cash-less toll highways along the way). Alternately, you can fly into Key West International Airport (EYW) which is served by several airlines including United/Silver Airways, Delta, USAir and Southwest. If you don’t mind coming into Key West, there is also the regular Key West Express ferry service (4 hours) that runs from Ft Myers. The Bahia Honda State Park is located at 36850 Overseas Highway on Big Pine Key. While they have onsite parking, it is known to fillup fast on summer weekends so plan accordingly.
Overall, Bahia Honda State Park is the 8th most popular snorkel dive spot of all 40 snorkeling dives in the Florida Keys.