Snorkelers have plenty of options in Cozumel , from cheap-and-easy snorkeling tours to renting gear and exploring on your own, right from shore.
Most dive shops  offer snorkeling as well as diving, usually visiting 2–3 sites for a half hour each (US$50–55 pp). Snorkelers often go out with a group of divers and either snorkel in the same general location or go to a nearby site while the divers are underwater. This can mean some extra downtime as divers get in and out of the water, but the advantage is that you typically go to better and less-crowded sites.
A number of shops sell snorkel tours from booths on the central passenger pier. These trips tend to be less expensive (though with larger groups) and can be booked right as you debark from the ferry—handy if your time is short.
A recommended shop/booth is Cha Cha Cha Dive Shop (Calle 7 btwn Avs. Rafael Melgar and 5 Sur, tel. 987/872-2331, www.chachachadiveshop.com , booth opens at 8 a.m.), which offers three-hour snorkeling trips on its glass-bottom boat for US$45 per person, including equipment and nonalcoholic drinks. You’ll snorkel for 30–45 minutes at each of three different sites. Its booth on the pier is easier to find than the actual shop, hidden down a narrow passage between souvenir stands and a tattoo parlor.
There are several terrific snorkeling spots near town and just offshore where you don’t need a guide at all. Cozumel’s boat drivers are careful about steering clear of snorkelers, but even so, do not swim too far from shore, look up and around frequently, and stay out of obvious boat lanes.
If you plan to do a lot of snorkeling, especially outside of established snorkeling areas, consider bringing or buying an inflatable personal buoy. Designed for snorkelers, they are brightly colored and have a string you attach to your ankle or to a small anchor weight, alerting boat drivers of your presence. Also be aware of the current, which typically runs south to north and can be quite strong.