A hundred people have fallen ill after contracting the norovirus at a beach in Kajaani, eastern Finland, according to local newspaper Kaleva.
City health officials say the patients were hit with intestinal ailments after swimming at the Kesäniemi beach in late July and early August. The beach is on Lake Sipinen, not far from the city centre.
Norovirus was not detected at the lakeshore in water tests carried out by local public safety officials, but has been found in stool samples from those affected.
City authorities shut down the beach when reports of people with stomach complaints began to surface. The virus causes symptoms including nausea, diarrhoea, and sometimes fever.
Local officials have advised people to avoid Kesäniemi beach until 23 August.
Health officials have issued a warning that the warm summer weather could increase the likelihood of contamination on beaches in general, according to the paper.