The bird flu virus has also been found in bean geese wintering in North Jeolla Province, following an avian flu outbreak among Baikal teals.
Tests of three dead bean geese at a reservoir in Gochang showed up the H5N8 virus, the same flu strain found in dead Baikal teals there, the agriculture ministry said Wednesday.
The ministry decided to beef up quarantine efforts.
Bean geese are migratory birds that breed in Europe and Russia and typically winter in Korea. Unlike Baikal teals that rest in flocks at three to four wintering sites, bean geese stay in small family groups in about 70 locations across the country.
Meanwhile, the ministry discovered three more dead Baikal teals at a lake between Gunsan and Seocheon and started tests to find out if they are infected with the flu virus.
The ministry aims to cull 410,000 chickens and ducks at 30 farms by Friday, with more than half already destroyed.