Around 50 people experienced sudden illness after swimming at Dalsjön in Dalsjöfors, Borås.

Residents, including Kim Fischer, reported symptoms like vomiting and fever on social media.

Despite recent water testing showing no abnormalities, the local authorities have initiated further investigations.

The cause of the outbreak remains unknown, but theories include contamination from algae or bird droppings.

Authorities advise against swimming in Dalsjön until the mystery is resolved.