Summer scenery is luminous in Yellowstone National Park, but under the surface lies an alternate reality. Photographer Brian Skerry entered the otherworldly ecosystem of Yellowstone Lake to explore unique spires formed by dormant hydrothermal vents thousands of years ago. Guiding him was Brett Seymour, pictured here, a diver and photographer for the National Park Service.
A change of altitude: As a kid, Skerry opted for rock kits over chemistry sets and hoped to become a geologist. Diving amid 11,000-year-old underwater hydrothermal formations was a dream assignment. But he had just returned from chasing dolphins in South Korea and was concerned about swapping sea level for some 7,700 feet above it: Yellowstone is the largest lake in North America at such a high altitude. How quickly would his body adjust? And in the depths, would he have the visibility for a good shot?
Essential packing list: To insulate himself from near-freezing water, Skerry wore a dry suit, which, unlike a wet suit, has room for thermal layers underneath. By the time Skerry dived off the boat, he was wearing a hundred pounds of gear.