Dolphins are highly intelligent and can be found all over the world in oceans, rivers and estuaries. As mammals, dolphins don't have gills so they can't breathe underwater. They must surface to inhale and exhale stale air, which they do through blowholes and not their mouths. How long they can hold their breath depends on the species; some can go for 3 to 7 minutes, while others can stay submerged for up to 20 minutes. Because they must always surface, half of dolphins' brains are always active, meaning they never completely fall asleep. Despite being able to exist in an array of environments and water temperatures, dolphins are threatened by a variety of human activities, such as hunting, pollution and fishing.

The pod of dolphins seen in today's image was photographed near Réunion, an island in the Indian Ocean off the east coast of Madagascar. A wide variety of marine wildlife can be found year-round in Réunion's deeper waters, including many types of sharks, orcas, humpback whales, sea turtles and of course, dolphins. The island's warm, tropical climate is ideal for these creatures, and spinner, bottlenose and rough-toothed dolphins swim in the island's crystal-clear waters.