Make your way to the diving and snorkeling center in Grand Case to meet your guide. Climb aboard your boat and head out of the marina, watching the coastline of St Martin's French side recede into the distance as you head out to sea.
Receive a safety briefing and intro snorkel lesson from your guide as you slip on the provided masks, fins, snorkel and flotation device. Learn about the island's remarkably diverse marine life and what types of animals and plants you are likely to see.
Arrive at Creole Rock, part of St Martin's Reserve Naturelle. Once the boat moors, slip into the shallow water to explore the sea grass beds, keeping an eye out for stingrays and peacock flounder. Clouds of sand give away the location of eagle rays in search of a meal. Float towards the rocky islet in search of other marine life like parrotfish and wrasses. Strong swimmers can head out further to catch a glimpse of porcupinefish, trumpetfish, spiny lobsters or even dolphins.
Back on the boat, head towards Turtle Reef and its two large rock formations sticking out of the ocean. Don your gear and jump back into the water, which ranges from 8 to 30 feet (2 to 10 meters) in depth. Look for green and hawksbill turtles, fan coral and the shy octopus. Swim among jawfish, toadfish and flying gurnards.
At the end of your 3.5-hour snorkeling excursion, climb back aboard for your ride back to Grand Case.