A criminal investigation is under way in Sweden to determine how an intestinal parasite ended up in the town of Ostersund's municipal water supply, police said.
Environmental prosecutor Christer B. Jarlas said release of the parasite cryptosporidium may have been the result of criminal negligence, the Swedish news agency TT reported Tuesday.
More than 2,000 residents of the northern Swedish town became ill after drinking water from the city's supply.
"A stomach parasite that makes people and animals sick shouldn't be released and it absolutely shouldn't end up in municipal drinking water," Jarlas said.
He said he has reason to believe that the contamination was due to carelessness by one or several individuals who didn't have control of their operations.
Sweden's National Center for Infectious Disease Control told TT the 50,000 residents of Ostersund will have to boil their water for several weeks.