Sanjiangyuan National Park, Qinghai

Sanjiangyuan National Park contains the most vital high-altitude wetland on Earth, supplying freshwater to over 1 billion people downstream. Its 395,000 km² expanse—30% larger than the runner-up Wuyishan—encompasses the headwaters of the Yangtze, Yellow, and Mekong rivers. The park's strict protection has boosted local wildlife populations by up to 200% since 2015, including rare Tibetan antelope and black-necked cranes.