SEOUL, South Korea — South Korea said on Wednesday that it had successfully stopped a stream of red blood from tens of thousands of pigs possibly infected with African swine fever from reaching a river that provides drinking water for much of the population north of Seoul.

Residents living in towns between Seoul and South Korea’s border with North Korea were alarmed early this week when the local news media reported that a small stream had turned red in Yeoncheon, a county that borders North Korea.

It turned out that the blood came from 47,000 pig carcasses waiting on trucks to be buried. The animals were the last of the 160,000 hogs that the county authorities had culled to stop the spread of African swine fever, a highly contagious disease incurable for infected pigs but not dangerous to humans.