The coastal plains are wide in the west and discontinuous in the east. A great majority of the population lives in the plains and lowlands. According to a United Nations Environmental Programme report in 2003, forest covers over 70 percent of the country, mostly on steep slopes. North Korea had a 2019 Forest Landscape Integrity Index mean score of 8.02/10, ranking it 28th globally out of 172 countries. The longest river is the Amnok (Yalu) River which flows for . The country contains three terrestrial ecoregions: Central Korean deciduous forests, Changbai Mountains mixed forests, and Manchurian mixed forests.