Cancún is one of the water-sports capitals of the world, and, with the Caribbean on one side of the island and the still waters of Laguna Nichupté on the other, it's no wonder. The most popular activities are snorkeling and diving along the coral reef just off the coast, where schools of colorful tropical fish and other marine creatures live.
If you want to view the mysterious underwater world but don't want to get your feet wet, a glass-bottom boat or "submarine" is the ticket. You can also fish, sail, Jet ski, parasail, or windsurf. If you prefer your water chlorinated, lots of hotels also have gorgeous pools -- many featuring waterfalls, Jacuzzis, and swim-up bars serving drinks with umbrellas. Several hotels offer organized games of water polo and volleyball as well as introductory scuba courses in their pools.
Since the beaches along the Zona Hotelera can have a strong undertow, you should always respect the flags posted in the area. A black flag means you simply can't swim at all. A red flag means you can swim but only with extreme caution. Yellow means approach with caution, while green means water conditions are safe. You are almost never going to see the green flag -- even when the water is calm -- so swim cautiously, and don't assume you're immune to riptides because you're on vacation. At least one tourist drowns per season after ignoring the flags.
Unfortunately Laguna Nichupté has become polluted from illegal dumping of sewage and at times can have a strong smell. In 1993 the city began conducting a clean-up campaign that included handing out fines to offenders, so the quality of the water is slowly improving. There is very little wildlife to see in the lagoon so most advertised jungle tours are glorified jet-ski romps where you get to drive around fast and make a lot of noise but not see many animals.
Although the coral reef in this area is not as spectacular as farther south, there is still plenty to see with more than 500 species of sea life in the waters. If you're lucky you may see angelfish, parrot fish, blue tang, and the occasional moray eel. But the coral in this area are extremely fragile and currently endangered. To be a good world citizen follow the six golden rules for snorkeling or scuba diving:
1. Don't throw any garbage into the sea as the marine life will assume it's food, an often lethal mistake.
2. Never stand on the coral.
3. Secure all cameras and gear onto your body so you don't drop anything onto the fragile reef.
4. Never take anything from the sea.
5. Don't feed any of the marine animals.
6. Avoid sunblock or tanning lotion just before you visit the reef.