All Dutch outdoor swimming spots are chemically polluted, study finds

A study by environmental organisation Natuur & Milieu and the Netherlands Institute of Ecology (NIOO-KNAW) has revealed that 100 percent of examined outdoor swimming spots in the Netherlands fail to meet chemical water quality standards, despite official safety ratings declaring them clear.

Official ratings hide toxic chemical cocktails

Local water authorities regularly test designated swimming sites across the country, publishing safety advisories on official platforms like zwemwater.nl. However, a joint study by Natuur & Milieu and NIOO-KNAW points out that current testing protocols focus almost exclusively on acute biological risks, such as E. coli bacteria and toxic blue-green algae (blauwalg).

This creates a misleading safety loophole. Locations like Amsterdam's Gaasperplas can achieve an "excellent" official safety rating while simultaneously containing 10 different chemical substances above legal limits. "The government only intervenes when there is too much blue-green algae and bacteria, but not with chemical pollution," Rob van Tilburg, programme director at Natuur & Milieu, told AD.

Testing limits & breaking European law

Beyond keeping swimmers in the dark, local authorities are treading on thin legal ice with EU regulators.

"The government measures whether there are chemicals in the water, but they are not obligated to report it," Koenraad Backers from Natuur & Milieu told NOS. "However, under the European Water Framework Directive (KRW), they are required to keep these substances below the set limit. Right now they are in violation, and the Netherlands will be called to account in 2027."

Researchers stress that a single swim will not cause immediate health issues. However, regular exposure leads to a build-up of toxic substances in the human body over time, increasing long-term risks of hormone disruption, weakened immune systems and cancer.

Rapid decline in water quality across city and countryside

A decade ago, 22 percent of tested locations met chemical quality standards. Today, that figure has dropped to 0 percent across all 262 sites examined by researchers.

The specific pollutants depend heavily on where people take a dip. In urban spots like Amsterdam, swimmers share the water with industrial smoke particles, soot and legacy boat paint (tributyltin) - a banned toxic substance that sits on lake beds until passing vessels churn it up. In rural areas, agricultural pesticides dominate, including imidacloprid, a chemical routinely found in dog flea collars.

Zaandam's Jagersplas holds the dubious title of the most polluted location in the country, containing 18 different chemical substances in excessive concentrations. Meanwhile, nutrient pollution from nitrogen and phosphorus remains stagnant, fuelling ideal conditions for toxic algae blooms after warnings were issued at dozens of Dutch swimming locations earlier this summer.

Environmental groups call for tighter controls and PFAS ban

To tackle the widespread contamination, researchers from Natuur & Milieu and NIOO-KNAW are calling on the Dutch government to target pollution directly at its source. Key demands include enforcing stricter industrial discharge permits, integrating chemical testing into regular public health updates and enacting an immediate ban on non-degradable "forever chemicals" like PFAS.

Environmental advocates also argue that regulatory bodies must account for popular unofficial urban swim spots, which currently operate in a legal blind spot when authorities grant industrial discharge permits. Without comprehensive monitoring and updated licensing, water quality improvements will remain stalled.

Autumn is here, the heatwaves have passed and the need to cool off has wavered for most. However, those planning to take one last dip in local lakes or canals should continue checking official platforms like zwemwater.nl for acute bacterial warnings, while keeping in mind that a clean bill of health does not mean the water is completely pure.