More than 400 fish species and green sea turtles live in this marine ecosystem at one of the best snorkeling spots in Hawaii.

Put on a mask, snorkel and fins, and jump into the crystal clear waters of Hanauma Bay to watch a colorful school of butterfly fish glide beneath you. Dive down to say aloha to the graceful green sea turtles and stop to examine the intricate formations of the living coral as you explore Oahu’s accessible marine ecosystem. You will not only have the chance to encounter creatures up-close, but can also learn about their biology and habitat in the Marine Education Center.

The perfect curve of Hanauma Bay is part of an eroded volcanic crater into which the ocean has eventually forced its way. The calm, nutrient-rich waters make it the perfect place for an abundance of marine life to flourish, and few places in the world can boast such a diversity of species so close to shore.

The preserve’s function is to protect this unique ecosystem, and when you enter Hanauma Bay, you first come to the Marine Education Center. The structure resembles the natural shape of a volcanic cave. As well as colorful murals depicting the marine life of the bay, you’ll see exhibits explaining the geography of the bay and the formation of coral reefs. There are also a number of interactive stations where you can try your hand at fish identification. A short film in the theater further explains the biodiversity of the area.

Pick up a laminated fish identification chart from the reception and walk to the beach or, for a small charge, ride the tram. After this, it’s all about floating and swimming in the water and seeing how many fish you can spot and name.

Hanauma Bay Nature Preserve is located 10 miles (16 kilometers) east of Waikiki, just off Kalanianaole Highway. It’s closed on Tuesdays. If you don’t have your own snorkeling gear, visit the rental shop near the Marine Education Center. You are permitted to bring your own food and drinks, and can also purchase refreshements from the snack bar.