Regional health authorities are advising residents to check water quality before swimming, as warm weather increases the risk of blue-green algae in popular lakes and outdoor spots.
Temperatures across North Holland are reaching summer highs, leading many people to seek out open water to cool off.
Health risks from toxic algae
Officials have issued warnings for several swimming locations across the province where blue-green algae has been detected, including sites in Spaarnwoude, Het Twiske, and the Amsterdamse Bos.
Blue-green algae, which is actually a type of bacteria known as cyanobacteria, thrives in warm, still water during dry spells.
Contact with contaminated water can cause skin irritation, nausea, headache, and stomach discomfort, while ingestions can potentially damage the liver or nervous system.
The bacteria is particularly hazardous to dogs, which often swallow water while swimming or lick their fur clean afterward.
Checking official designated waters
Swimmers are encouraged to stick strictly to official designated bathing sites where the water is routinely monitored for bacterial growth and pollution.
Local authorities update the national platform zwemwater.nl regularly to display real-time safety warnings, closures, and water condition reports.
While cooler weather and higher winds later in the week may help circulate water in some areas, health hazards often persist until temperatures drop significantly.