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.
Amblyrhynchus cristatus is not always black; the young have a lighter coloured dorsal stripe, and some adult specimens are grey, and adult males vary in colour with the season. Dark tones allow the lizards to rapidly absorb heat to minimize the period of lethargy after emerging from the water.
Breeding-season adult males on the southern islands (Española, Floreana and nearby islets) are the most colourful and will acquire red and teal-green colours, while on Santa Cruz they are brick red and black, and on Fernandina they are brick red and dull greenish.