Heavy rain sends untreated sewage into Danish bathing waters

Danish sewers cannot handle extreme downpours, forcing utilities to divert untreated wastewater—including toilet water—into the sea after heavy rain, according to a report by public broadcaster DR.

Record heat over the weekend drew many to the beaches, but water quality was poor at several locations on Sunday, with red flags raised along much of the Øresund coast, including at Bellevue Strand and Nordhavn in Copenhagen.

Anders Erichsen, director of environmental science at DHI, which advises municipalities and utilities on wastewater, said the choice is stark: either let sewage back up into streets and basements, or release it into bathing waters.

“It’s almost impossible not to discharge wastewater into the sea after heavy rain,” Erichsen said. The risk of overflows is highest when large amounts of rain fall in a short time, and he warned that red flags could reappear this summer.

Swimming in contaminated water may cause stomach upset within a couple of days, though illness depends on bacterial concentration, Erichsen added. Those who swam on Sunday may still avoid consequences.

Urban areas are particularly vulnerable because pavement and sidewalks funnel more rainwater directly into sewers. Real-time water quality updates are available on badevand.dk, which was temporarily down on Sunday due to high traffic.