Cocos Island: When to Go for Hammerheads and Whale Sharks

Rising from the open Pacific, 550 kilometers off Costa Rica’s coastline, Cocos Island is a legendary destination for divers in search of raw, pelagic action. Designated a UNESCO World Heritage Site, this remote volcanic island is surrounded by nutrient-rich waters that attract some of the largest concentrations of marine megafauna on the planet. Schooling hammerheads, hunting tuna, cruising whale sharks, and cleaning-station mantas — all make appearances in this protected marine wilderness. Accessible only by liveaboard, diving in Cocos is an expedition, and the timing of your trip matters. Here’s everything you need to know about the best time to dive in Cocos Island.

Quick Summary

Best time to dive: June to November (more action); December to May (calmer seas, better visibility)
Water temperature: 22–28°C (72–82°F)
Visibility: 15 to 30 meters (50–100 feet), depending on season
Marine highlights: Scalloped hammerheads, whale sharks, tiger sharks, mantas, dolphins, sailfish
Season type: Two distinct seasons: wet (green) and dry

Diving Seasons in Cocos Island

Wet Season (June to November)

This is the best time to dive in Cocos Island if your goal is maximum pelagic action. Stronger currents, nutrient upwellings, and lower visibility create the ideal environment for large marine aggregations. Scalloped hammerheads gather in enormous schools above seamounts like Bajo Alcyone and Dirty Rock, while tiger sharks and Galápagos sharks patrol the depths.

This season also increases the chance of whale shark encounters, particularly in August to October. While visibility may drop due to plankton blooms and surface runoff, the tradeoff is more activity and biodiversity. Divers should expect occasional rain, rougher crossings, and more demanding diving conditions, but for big-animal lovers, it’s worth it.

Dry Season (December to May)

The dry season brings calmer seas, warmer water, and better visibility, making it the preferred window for underwater photographers and first-time visitors to Cocos. Hammerheads and reef sharks are still present, especially at Manuelita Channel and Viking Rock, and conditions are generally more comfortable for liveaboard travel.

During this time, divers may also encounter marlin, tuna, mobula rays, and occasionally dolphins, especially in deeper blue waters near drop-offs. Surface conditions are typically more stable, and sunlight penetration creates vivid underwater scenes perfect for wide-angle imaging.

Marine Life Highlights

What sets Cocos apart is the density and diversity of large predators. You’re almost guaranteed to see sharks on every dive, with many sites offering sightings of hammerheads, silky sharks, blacktips, and Galápagos sharks within the same dive. Tiger sharks have become increasingly common in recent years, often seen gliding through shallows at sites like Dirty Rock and Manuelita Outside.

Other highlights include whale sharks, which are most frequently observed during the late wet season months, and schools of eagle rays, mobula rays, and trevally. Green turtles, moray eels, and octopuses round out the reef life in areas like Dos Amigos Grande and Lone Stone. Due to the park's remoteness and protection, fish populations are exceptionally healthy and undisturbed by human presence.

Photography Tips by Season

June to November is best for capturing dense shark schools and dramatic big-animal scenes. However, strong currents and lower visibility require fast shutter speeds, wide-angle lenses, and powerful strobes. Many divers shoot at Alcyone, using reef hooks to remain stable while hammerheads pass overhead.

During the dry season, the calm seas and sunlight provide ideal conditions for blue water shots, especially with mantas or tiger sharks. Manual white balance is useful for minimizing green/blue hues, and a red filter helps with natural light shots during surface intervals or snorkel sessions.

Dive Travel Tips for Cocos Island

Liveaboards only: Cocos is only accessible by liveaboard, with 10–12 day itineraries departing from Puntarenas, Costa Rica.
Booking in advance: Due to the park’s popularity and limited seasonality, trips fill up quickly. Book 9–12 months in advance, especially for the whale shark season (August–October).
Experience level: Most operators require divers to have 50–100 logged dives, Advanced Open Water certification, and good current-handling skills.

Liveaboards and Dive Operators

Liveaboards offer expert guides, large dive decks, camera stations, and nitrox for extended bottom times.

Itineraries typically include multiple dives at Alcyone, Dirty Rock, Manuelita, and Dos Amigos, as well as exploratory dives, depending on the conditions. Some trips offer rebreather support, deep diving, and optional submersible excursions on special charters.

Other Top Dive Destinations by Season

If you're looking for more remote, big-animal dive destinations, consider:

When to Dive in Cocos Island

The answer depends on what you're after. From June to November, the waters deliver peak predator action, featuring hammerheads, whale sharks, and tiger sharks in breathtaking numbers. From December to May, the waters offer clearer visibility and calmer seas, making them ideal for photographers and divers seeking comfort without compromising on wildlife encounters. Either way, Cocos Island promises the kind of wild, untamed diving that reminds us what the ocean used to be, and still is, in this protected corner of the Pacific.