In New Zealand’s Nelson Lakes National Park, about 1,200 meters (4,000 feet) above sea level and a two-day hike from nearest civilization, lies Rotomairewhenua, or Blue Lake. (CNN/Janet Newel) ...

Editor’s Note: Call to Earth is a CNN editorial series committed to reporting on the environmental challenges facing our planet, together with the solutions. Rolex’s Perpetual Planet Initiative has ...