City council officials carry out regular checks of Malmö's public bathing spots, and the latest inspection revealed algal bloom at every single site.
Not all algal bloom is harmful, but some could contain toxic cyano bacteria. Swallowing the water could cause nausea, vomiting, diarrhoea, stomach pain, headache or skin irritation.
Children, dogs and people with underlying health conditions are particularly vulnerable.
Because the algae can shift quickly, it is impossible to say how long the swimming advisory will remain in place.
Malmö residents can keep up to date with current beach advisories on the city council's website.