The sweeping color of sea and sky, blue is a common thread in nature, seen in the cerulean of a whale shark (pictured here),
the indigo of a stormy night, and the cobalt of a peacock's feathers.
Over the centuries, the hue has come to represent calm, cold, mysticism, and sadness.
A thick, swirling school of black fin barracuda plies the blue waters off Sipadan Island, Malaysia.
The fish are formidable predators, but they sometimes gather in groups for protection against sharks higher up on the food chain.
A group of chinstrap penguins lines the edge of an iceberg adrift in Antarctic waters.
Chinstraps are among the most abundant penguins, and some colonies live on floating icebergs.
A polar bear leaps off of sea ice near Devon Island in the Canadian Arctic.
Strong swimmers, polar bears have slightly webbed paws to aid in paddling.
A blue pool on Root Glacier in Alaska's Wrangell-St. Elias National Park reflects the bulk of towering Donoho Peak. The massive ice sheet is a popular excursion in the park.
These distinctive webbed feet belong to a blue-footed booby of the Galápagos Islands. The bluer, the better: Courting males show off with a high-stepping strut—and those with brighter feet are more attractive to potential mates.
Some of nature's intricate patterns are on display in this magnified view of the mineral azurite.
The bright blue mineral was once used to make paints and may still be found in jewelry.
Holidaymakers take the plunge and enjoy a twisting, turning trip down an waterslide.
Frost covers the brilliant blue leaves of lush ferns in New Zealand's Fiordland National Park.
The park is an isolated wilderness that's home to more than 700 plants found nowhere else in the world.
Ice, seen from below, covers the surface of the Arctic's Beaufort Sea.
The sea is found north of Alaska and Canada.