Objective To investigate and analyze the causes of a drinking water pollution incident in a township,so as to provide reference for the disposal of sudden water pollution incident. Methods A retrospective study was conducted to investigate the epidemiology of infectious diarrhea among residents of BY Town,and an environmental hygiene investigation was carried out on the waterworks of BY Town.Bacterial culture and RT-PCR methods were used to detect intestinal pathogens in patients' anal swabs,feces,and related water samples such as the raw water,treated water,and peripheral water of BY town's waterworks. Results From August 17 to 28,2020,BY Town experienced a total of 598 cases of infectious diarrhea,of which 128 patients were tested for pathogens.Shigella was detected in 107 patients with a positive rate of 83.59%.The cases were mainly concentrated in August 19 to 23,and peaked on August 20.The clinical symptoms were mainly abdominal pain,diarrhea and fever.Most of them were under 14 years old (accounting for 55.9%).The distribution of the cases was consistent with the water supply scope of a waterworks.Cases were found in all villages of BY Town,with the highest incidence in BY street (accounting for 5.0%).The water quality of the raw water was detected as class IV,which did not meet the drinking water source standard.Shigella was cultivated in the clean water pool of the waterworks. Conclusion This incident is an outbreak of the epidemic caused by Shigella contamination of drinking water.