South Korean authorities recovered 15 suspected North Korean landmines from several coastal locations in the northwestern border county of Ganghwa, officials said Friday. Ganghwa civil defense chief Choi Young-ran said the mines were found between July 23 and August 3 and were believed to have floated in from the inter-Korean border area during the monsoon season and recent heavy rainfall. All 15 mines were safely removed.

The Demilitarized Zone, established after the 1950-53 Korean War, divides North and South Korea and is among the world’s most heavily mined areas. Military information cited by Yonhap estimates that about 800,000 landmines are buried in and around the DMZ. Most were laid during the war, although mine-laying has continued in recent years.

South Korea’s military warned last month that explosives carried by swollen border rivers into low-lying areas could cause major damage. Local officials said Wednesday that the possibility of more mines washing ashore could not be ruled out. A Ganghwa resident said the risk could endanger people who collect shellfish by hand, while also raising concerns about local tourism.