Eco-tourism sites in and around Cancun include:
Sian Ka'an Biosphere Reserve, Isla Contoy, Garrafon National Park, Isla Mujeres
Rio Lagartos, The Dr. Alfredo Barrera Marin (nature trail), Croco Cun, Acuario Playacar, Aviario Xaman-ha, Chancanaab National Park, Cozumel, Mangrove, Forest Jungle Tours, Xcaret, Xel-ha, Xpu-ha.
Sian Ka'an serves as home for over 345 species of birds, all of the endangered cat species (jaguar, puma, ocelot, and margay), spider monkeys, crocodiles, manatees, and various types of sea turtles.
Isla Contoy is an island just a short boat ride from Isla Mujeres and is an undisturbed natural habitat for birds such as the pelican and egret.

Croco Cun is a large crocodile farm that is open to the public. Just next door is the Acuario Playacar, a small aquarium that displays what snorkelers in and around Cancun would see.
Jungle tours are conducted through the dense mangrove forests just outside Cancun. Each person uses a two-person speedboat to follow the guide through the lagoon to anchor near the Punta Nizuc Reef. From there the group snorkels out to the reef and enjoys the wildlife native to the Punta Nizuc.
Xcaret is a huge nature area 45 miles south of Cancun featuring Mayan temples, a snorkeling lagoon, aviary, butterfly pavilion, and underground river. You can float down the underground river and enjoy the unique coral formations and fish that live there.

Xpu-Ha is one of the newest additions to the eco-attractions near Cancun. It contains 99 acres of jungle, sinkholes, pristine beaches, wetlands and a coral reef. One price includes transportation from Cancun, guided tours, beverages, sailing excursions, lockers, showers and more.
With all the other options available try not to overlook the obviously wonderful snorkeling and diving just outside your hotel in Cancun. If you plan on diving we suggest getting certified before you go. You can, however, become certified at one of any number of dive shops in Cancun while on vacation.