When the Caribbean reefs are clearest
On the Riviera Maya, the reef sits close to shore from Puerto Morelos down past Tulum, and water clarity follows the rain rather than the temperature. December to April brings the steadiest conditions: less runoff from the jungle, lighter winds and flat water inside the reef crest. May and June stay warm and usually calm, but afternoon showers start. September and October are the wettest and windiest months, when nortes can shut the beach for a day or two and visibility drops. August is warm and busy but perfectly swimmable, especially early morning before the tour boats arrive.
Water temperature moves little: roughly 26°C in winter to 29°C in summer, so a shorty wetsuit is enough for long sessions. Off Cozumel, the Palancar and Columbia reef systems are better reached by boat, and the sheltered leeward side often stays clear when the mainland coast is choppy. If I were booking a first reef trip, I would choose late January to March and stay in Puerto Morelos or Akumal, where you can walk from a small hotel to the water without a transfer.
Pacific and Sea of Cortez options
The Pacific side works on a different calendar. In Baja California Sur, the Sea of Cortez around La Paz and Isla Espiritu Santo is calmest from May to October, when the north winds ease and the water warms to around 26°C. Cabo Pulmo, north of San José del Cabo on the East Cape, is a protected marine park with living coral and a dense fish population; access is through the village, and dive shops there run guided snorkel trips. Winter brings cooler water and stronger wind, though humpback whales make December to March worthwhile for boat days.
On the Pacific coast proper, around Sayulita and Puerto Vallarta in Nayarit and Jalisco, visibility is more variable because river runoff and swell stir the shallows. The dry season, November to May, is the reliable window. For families, the Sea of Cortez beats the open Pacific: calmer water, warmer mornings and beaches at Balandra and Playa El Tecolote within a short drive of La Paz hotels. I would skip open-ocean snorkelling near Puerto Vallarta in September, when rain runoff clouds the bays.
Etiquette that protects the reef and your welcome
Mexican reef areas are regulated, and the rules are enforced rather than decorative. In the Cozumel Reefs National Park and at Cabo Pulmo, you snorkel with a licensed guide, wear a life jacket in marked zones, and keep a hand's distance from coral at minimum — touching breaks the polyps and removes the mucus layer that protects them. Reef-safe sunscreen without oxybenzone and octinoxate is now required in many parks and marine areas; bring it from home, as local stock is limited. Never stand on coral, chase turtles or feed fish, and keep fins off the sand where seagrass beds grow.
Local operators depend on repeat visitors, so small gestures matter. Ask before entering a fishing village's beach access, pay the small park or pier fees where they are posted, and tip guides and boat crews in pesos. Learn a few words of Spanish — buenas días, por favor, gracias — and use them. Book tours directly with cooperativas or established dive shops rather than beach touts, which keeps money in the community. If a guide says the water is too rough, believe them; rescheduling costs an afternoon, not a reef.
Where to base yourself and what to book
For Caribbean snorkelling, base in Puerto Morelos for easy shore access and a compact village of small hotels, or in Akumal for turtle grass bays and a short drive to Tulum's cenotes. Cozumel suits boat-based reef trips and has the widest range of dive operators. On the Pacific side, La Paz is the strongest base for Sea of Cortez trips, with malecón hotels, seafood markets and day boats to Espiritu Santo; Cabo Pulmo village has limited beds, so book well ahead if you want to stay inside the park.
Book accommodation with free cancellation and a location within walking distance of the beach or marina, since parking near popular access points fills early in high season. Check that your hotel can store or rinse gear, and confirm tour pickup points before arrival. Shoulder months — late April and early November on the Caribbean, June and October in Baja — give good water with fewer crowds. Skip package tours that promise five reef sites in one day; two unhurried sessions with a good guide will show you more.