The marine iguana is a species of lizard endemic to the Galapagos Islands. It is the only lizard in the world able to live and feed exclusively in the sea. It has a unique appearance with its dark color, ranging from dark gray to black, and its flattened shape. Males have a spiny dorsal crest and a larger head than females. Marine iguanas also have sharp claws, long tails and a muscular body. Unlike other lizards, the marine iguana evolved to live in the water and is therefore primarily a marine animal. It spends much of its time in the Pacific Ocean feeding on underwater algae. However, they also come out on rocks and beaches to warm up in the sun and to lay their eggs in the sand. Marine iguanas are solitary animals, but they sometimes gather in large numbers on rocks and beaches to warm up. When in the water, they may remain submerged for long periods, up to an hour or more, holding their breath. They can also dive to depths of up to 100 feet to feed on algae.

Marine iguanas are active year-round, but the best time to see them depends on what you want to see. If you want to see the males in courtship and territorial combat, then the dry season (June to December) is ideal. If you want to see the females laying their eggs, then the wet season (January to May) is more appropriate. Marine iguanas breed in groups on beaches. Males compete for females, who lay their eggs in holes dug in the sand. Females usually lay 2-5 eggs that hatch about 90 days later. The young marine iguanas must break out of the sand and make their way to the sea to begin their life in the water.

There are several islands in the Galapagos where marine iguanas can be seen, including Isabela, Fernandina, Santa Cruz, Española, San Cristobal and Santiago. Each of these islands offers a unique wildlife viewing experience.