A river near the inter-Korean border turned red with the blood of pigs slaughtered as Seoul attempts to curb the spread of African swine fever.
South Korea has culled around 380,000 pigs since the first case of the haemorrhagic disease -- which is not harmful to humans but is highly infectious in swine -- was reported in September.
Pig cases are nearly always fatal and there is no antidote or vaccine, with the only known way to prevent the disease from spreading being a mass cull of livestock.
A local NGO said that heavy rains last week caused blood from a burial site near the inter-Korean border -- where some 47,000 pig carcasses were piled up -- to seep into the Imjin River on Sunday, turning some of the stream red.
"It made many people living in the area anxious and worried," Lee Seok-woo, who heads the NGO Yeoncheon Imjin River Civic Network, told AFP.
"What was also hard to endure was the odour. I heard many farmers couldn't work because of the unbearable smell. This should not have happened."