If you read our guide to diving San Carlos in February, you know that winter brings crisp, cool water and crystal-clear visibility. But as the calendar flips to July and August, the Sea of Cortez undergoes a radical transformation. The Sonoran Desert heats up, the water temperatures soar, and the ocean kicks into overdrive.
Summer diving in San Carlos is not for the faint of heart when you are topside, but the moment you giant-stride into the water, you are rewarded with one of the most vibrant, action-packed marine environments on the planet. Here is exactly what to expect if you are planning a dive trip in the heat of summer.
The Conditions: Bathwater and the “Green Soup”
Let’s talk about the two biggest changes you will experience in July and August: temperature and visibility.
- The Temperature: The water is glorious. You can expect temperatures to range from 80°F to 86°F (27°C – 30°C). The heavy 7mm wetsuits and hoods are banished to the closet. You will be perfectly comfortable in a 3mm full suit (which we still recommend for protection against scrapes and jellyfish) or even a rash guard and board shorts.
- The Visibility: Here is the honest truth: summer is not the time for 100-foot, gin-clear visibility. The water warms up and the sunlight triggers massive plankton blooms. Visibility often drops to the 30-to-50-foot range and sometimes less, and the water can take on a greenish hue.
Why lower visibility is a good thing: That “green soup” is the base of the entire oceanic food chain. The plankton is what attracts the massive schools of baitfish, which in turn attract the giants of the sea. You sacrifice a little visibility for a massive explosion in biomass.
The Main Event: Pelagics and Feeding Frenzies
Because the water is so nutrient-rich in the summer, the offshore sites and the waters around Isla San Pedro Nalasco become a high-stakes hunting ground.
- Bait Balls: Summer is prime time for bait balls. The massive schools of sardines and anchovies are hunted relentlessly by super-pods of Common Dolphins, diving pelicans, and sea lions. Watching the water boil on the surface before your dive is a daily occurrence.
- Manta Rays and Mobulas: The plankton brings in the filter feeders. While gigantic Oceanic Manta Rays are a rare and lucky treat, you have an excellent chance of encountering massive squadrons of their smaller cousins, the Mobula Rays, soaring through the water column like underwater birds.
- Sea Lion Breeding Season: At the island rookery, summer is breeding season. The massive, 800-pound dominant bulls are establishing their territories and barking aggressively to protect their harems. It is a thrilling display of raw nature. (Note: We give the bulls a very wide berth during this time, focusing our dives on the playful juveniles and females on the periphery of the colony.)
Managing the Topside Heat
While the water is perfect, the topside air temperatures in San Carlos during July and August are hot. Expect daytime highs in the 90s to low 100s°F (35°C – 40°C), often with increased humidity.
To keep your trip safe and comfortable, you need to manage the heat:
- Dive Early: We schedule our boat charters early in the morning to beat the midday heat. The ocean is usually calmest at dawn, and you’ll be back at the marina before the sun reaches its peak.
- Hydrate Obsessively: Dehydration is the number one cause of decompression sickness and general fatigue. Drink water constantly on the boat, even if you don’t feel thirsty.
- Seek Shade: Stay under the canopy of the dive boat during surface intervals. Bring a wide-brimmed hat, polarized sunglasses, and reef-safe sunscreen.
- Siesta Time: Do what the locals do. After your morning dives, grab some fish tacos for lunch and retreat to the air conditioning of your condo or hotel for an afternoon siesta.
The Perfect Summer Specialty: Night Diving
Because the afternoons are so hot, summer is the absolute best time to earn your SSI Night Diving and Limited Visibility specialty.
When the sun sets, the desert cools down beautifully. Entering the 85°F water at night feels like stepping into a warm bath. You escape the blistering sun entirely and get to witness the incredible nocturnal shift of the reef, from hunting octopus to the dazzling display of bioluminescence.
The Verdict
Summer in San Carlos is for divers who want to be in the center of the action. If you love warm water, don’t mind a little green tint, and want to see the food web operating at maximum capacity—from tiny plankton to cruising rays and boiling bait balls—July and August deliver an unforgettable, high-energy adventure.
Ready to ditch the thick wetsuit and dive the World’s Aquarium? Contact us to book your summer boat dives and night diving adventures!