Dutch authorities have issued safety warnings for approximately 40 official wild swimming locations due to the presence of blue algae. Two locations have been completely closed to swimmers.

Blue algae, a bacterium that can produce toxins harmful to humans, thrives in conditions common in the Netherlands. Exposure to blue algae can cause symptoms such as nausea, diarrhea, and skin rashes.

In addition to blue algae, poor water quality has led to swimming advisories at another 42 locations. The presence of fecal bacteria, which can cause stomach upsets, is a primary concern. Other hazards include PFAS and sharp Japanese oysters.

Authorities advise swimmers to exercise caution and use common sense. Swimmers should avoid water with a blue, green, brown, or red oily layer, as this can indicate the presence of blue algae.

The zwemwater.nl monitoring website and the water boards’ Zwemwaterapp provide updated information on water quality at swimming locations.

The two locations where swimming is currently prohibited are a natural pool at the De Betteld holiday camp in Gelderland, where “extremely high PFAS levels” were detected, and It Nanneveld in Friesland, where ongoing construction activities make swimming unsafe.

Data from the European Environment Agency suggests that Dutch wild swimming water quality ranks among the poorest in Europe. The prevalence of inland and nearly stagnant water bodies contributes to the proliferation of bacteria.