evidence: The Yalu River is the longest river in North Korea, stretching 491 miles (790 kilometers). It begins on Paektu-san and flows southwest to the Yellow Sea. The Tumen River also begins on Paektu-san; it flows east into the Sea of Japan. [...] North Korea has nine national parks, the largest of which is Mount Kumgang National Park. But the DMZ between North and South Korea may be the peninsula's most important nature preserve. Since 1953, the DMZ has been considered neutral territory that no country owns; it’s patrolled by North Korea on one side and South Korea and the United States on the other, but few people are allowed inside. As a result, the DMZ is one of the most pristine nature preserves in Asia. The area is home to Asiatic black bears, red-crowned cranes, and long-tailed gorals (a species of wild goat). Overall, the DMZ is estimated to be home to some 70 species of mammals, more than 300 birds, and about 3,000 plants.