The marine iguana (Amblyrhynchus cristatus) is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The iguana can dive over 30 ft (10 m) into the water. It has spread to all the islands in the archipelago, and is sometimes called the Galápagos marine iguana. It mainly lives on the rocky Galápagos shore, but can also be spotted in marshes and mangrove beaches. Marine iguanas show their color as they mature – the young are black, while adults range from red and black, to black, green, red and grey, depending on the island, with Española marine iguanas being the most colorful of all, and earning them the nickname “Christmas Iguanas.”
Reference - Wikipedia: http://www.galapagos.org/about_galapagos/reptiles/