Swimming is ideal in the calm corners of the Bahías de Huatulco [1]. Especially good swimming beaches are at Playa Entrega [2] in Bahía Santa Cruz and Bahía El Maguey.
Generally clear water makes for rewarding snorkeling off the rocky shoals of all of the Bays of Huatulco [1]. Local currents and conditions, however, can be hazardous. Novice snorkelers should go on trips accompanied by strong, experienced swimmers or professional guides. Although rentals are generally available, best be prepared with your own equipment.
Huatulco scuba divers enjoy the services of well-equipped and professional Hurricane Divers scuba shop (tel. 958/587-1107, email [at] hurricanedivers [dot] com, www.hurricanedivers.com [3], 9 a.m.–6 p.m. Mon.–Fri., 9 a.m.–4 p.m. Sat.), in the small complex between the Santa Cruz main beach and boat harbor. They start novices out with a pool mini-course, followed by a three-hour ($95) resort dive in a nearby bay. Snorkelers go for about $60, with good equipment furnished. Hurricane Divers’ (PADI) open-water certification course takes about four days and runs about $340, complete. With your open-water certificate, you are qualified for the advanced (two-tank $120) dives. After that, you may be ready for more advanced trips, which might include local shipwrecks, night dives, and marine flora, fauna, and ecology tours.
Alternatively, try very experienced (since 1988 in Huatulco) Buceos Sotavento, which offers similar (PADI) services. Contact them at the Plaza Oaxaca complex (upstairs, shop #18, on the Crucecita plaza, southwest corner of Flamboyan and Gardenia, tel./fax 958/587-2166, scubasota [at] hotmail [dot] com, www.tomzap.com/sotavento.html [4]) or in Tangolunda (across from the Hotel Barceló, tel. 958/581-0051, cell tel. 044-958/587-7441).
Links:
[1] http://www.moon.com/destinations/oaxaca/pacific-resorts/bahias-de-huatulco
[2] http://www.moon.com/destinations/oaxaca/pacific-resorts/bahias-de-huatulco/exploring-bays-huatulco/west-side-bays
[3] http://www.hurricanedivers.com
[4] http://www.tomzap.com/sotavento.html