Warm weather? Then it is tempting to cool off in nearby water. At 240 swimming locations, both inland and along the coast in the Netherlands, we know whether or not the water there is safe through biweekly inspections by Rijkswaterstaat. The results of these tests can be viewed on a map at swimmingwater.nlor on this map:
Article continues under the card.
Canals, pools and streams are not on the map: often the water quality is not checked there. NRC lists for you how you can assess as well as possible whether water is safe enough for swimming.
Study the water surface
If there is a paint-like green or brown layer on the surface, swimming is a bad idea, says Miquel Lurling, blue-green algae expert and associate professor at Wageningen University and Research. Such a layer is created by an accumulation of bacteria and/or algae. “If that layer remains long enough and a bluish glow appears in the water from cracks, you know for sure that it is blue-green algae.”
Sometimes there is duckweed, blossom or non-dangerous thread algae on the water. The difference with, for example, blue-green algae is not always clear. To this end, an app was developed in the United Kingdom by the Center for Ecology and Hydrology: the Bloomin’ Algae App, which now also has a Dutch version. “Swimmers can upload photos of the water or the layer on the water. Experts from Wageningen University and Research then assess the photo and indicate as best and as quickly as possible whether they see any reason not to swim there,” says Lurling.
If mice have had a stroke, blue-green algae can save dying nerve cells. How does that work with people? Read it here: Blue-green algae can save the brain after a stroke – in theory
Watch out for further discoloration in the water
Discoloration of the water deeper than the surface can also indicate the presence of bacteria and algae. For those who doubt whether the discoloration really indicates poor quality, Lurling has a handy rule of thumb: “If you are in water up to your waist, you should still be able to see your feet. If that is not the case, it is better not to swim further.”
Incidentally, there is another reason not to swim in water where the bottom is not visible: you cannot see obstacles. “Sometimes I see children jumping off a bridge into the water, not knowing what’s underneath. That can be very dangerous,” warns Lurling.
Swimming is good for you, if you do it wisely. Read all about why swimming is such a great form of exercise for your body: Swimming is good for everyone.
How is the smell of the water?
Polluted water often does not smell so pleasant. “Water that contains blue-green algae can smell a bit sulfurous, especially if there is a lot of it,” says Lurling. Even without blue-green algae, smelly water is often bad news. “Stank can also come under the surface from dead animals, for example.”
Pay attention to where it is forbidden to swim
The quality of the water is not the only determining factor whether you can swim safely. A strong current in the sea, passing shipping traffic and mooring places for ships can also pose a danger to swimmers. If you go swimming in these places, you risk a fine of 150 euros.
Not sure if the water you want to swim in falls under the above points? Then check if you see signs that are on the Boat storage card standing, a map compiled by Rijkswaterstaat and the provinces, among others. Use the signs to determine whether or not swimming is allowed. No signs? Swimming at the locations on the map in this article and the one on swimmingwater.nl is allowed anyway, if the quality is good enough.
For swimming in the sea, first of all it is best to keep an eye on the flags on the beach to determine whether it is safe. Although beaches are not obliged to use such flags, you will see them at most seaside resorts. An overview of the meaning of the flags can be found at swimmingwater.nl . It is also good to be aware of other dangers in the sea. Lifeguards explain exactly what those dangers are in this NRC article from 2020: The current pulls you down in no time.
Don’t just jump into the city canal
Whether swimming is allowed in city canals depends on the location. Sometimes parts of a city canal belong to a waterway, or there are mooring places along the canal. You are not allowed to swim in such places. There are usually no explicit rules about other parts of the canal, but it is generally known that quite a few bicycle wrecks and other coarse debris and filth end up in city canals. Municipalities are responsible for clearing these, so that water safety can be guaranteed.
For example, the municipality of Amsterdam indicates that it can guarantee water safety at official bathing water spots, including some parts of the canals. “In other places where there is also a lot of swimming, we fish up the bulky waste before the start of the swimming season, but there cannot be guaranteed that it is safe,” a spokesperson for the municipality said. These places are not under constant control. The municipality says that most canals are unsuitable for swimming anyway, “because the waters are busy and the canals are too narrow to be able to swim.”
The water in the Amsterdam canals has become increasingly cleaner in recent decades, says Tim Leeuwerke, spokesperson for the Amstel, Gooi en Vecht water board. This required, among other things, two major changes: moving the sewage treatment plant to the Westelijk Havengebied in 2006 and connecting houseboats to the sewer, the last of which was completed in 2018.
“Relocation of the purification has ensured that the Amstel in particular has become a lot cleaner,” says Leeuwerke, “and by no longer letting houseboats discharge their dirty water directly into the canals, the quality in various places improved significantly.” In the years before 2006 and other years in between, smaller-scale actions were also taken to improve water quality, Leeuwerke emphasizes.
Be extra vigilant in hot weather and standing water
Due to the years of supply of nutrients such as phosphorus and nitrogen via the soil and the air, the water of many lakes and puddles has become turbid and nutrient-rich. Aquatic plants do not or hardly survive there, due to a lack of sunlight: algae takes over. Blue-green algae also thrive mainly in such turbid, nutrient-rich systems. Especially in warm weather, without wind. During such periods, therefore, be extra alert to the water quality, which can deteriorate rapidly.
Incidentally, the quality of many waters in the Netherlands leaves something to be desired. You can read more about it in this article: Clean water is still a long way off in the Netherlands.