Now that the summer holiday period is starting, the crowds in swimming water are increasing again. The poisonous pieterman sometimes makes a victim in salty seawater, but risks can also be found in fresh water. And that does not always come in the form of a fish.
Hikers in Beuningen, Gelderland, looked up strangely last week when they saw a huge catfish lying on the beach. The European catfish is the largest freshwater fish in the Netherlands and increasingly appears in the Netherlands.
The wildest stories are circulating about the predator fish, says Onno Terlouw, sport fisherman and spokesperson for Sportvisserij Nederland. "They are huge beasts and they look very dangerous. It is known that they can pluck pigeons and water birds from the surface and swallow them all at once. But they are fairly innocent for humans," Terlouw says.
The European catfish can be up to 2 meters long. (Photo: Thinkstock)
Attack by a pike once a year
Unlike in the salty seawater, where the poisonous pieterman sometimes makes a victim, there are no poisonous or dangerous fish in Dutch freshwater, says Terlouw. "Very occasionally it happens that a swimmer is attacked by a pike or perch, when they protect their nest in the spring. Something like that happens once a year. The chance that you get a hook in your finger while fishing is greater "
Toxic things in Dutch natural water that can pose a health risk come from much smaller animals. For example cyanobacteria, better known as blue algae. "This can cause skin rashes, headaches and nausea," says Thecla den Hoed of the Delfland Water Board.
Blue algae thrive in warm, stagnant water that is rich in nutrients from, for example, fallen leaves and goose poop. "They emerge precisely during a period when a lot of people go swimming," says Den Hoed.
Non-hazardous leech may remain in place
In the summer, the water boards check the 724 Dutch swimming pools for pollution every month. Places with poor water quality are checked once every two weeks. "We check for things that can bother you as a swimmer," says Den Hoed. "For example on E. coli, the shit bacteria. Everyone knows that it can make you sick."
Issues that do not entail health risks for people, but that swimmers may experience as annoying, are not included in the water quality assessment. Visitors to the Henschotermeer in Utrecht regularly complain about leeches sticking to the skin in the water. During the inspection it turned out to be a non-hazardous species and therefore the water quality carries the 'excellent' qualification.
Blue-green algae in Eindhoven's Meerland park in August 2018. (Photo: NU.nl/Ralph de Pagter)
What is checked for?
- Blue algae: causes skin irritation, headache, nausea, diarrhea or eye inflammation
- E. coli (the shit bacteria): causes diarrhea, fever and vomiting
- Botulism bacterium: many water birds and fish die, the dead animals pose human health risks
- Intestinal enterococci: harmless to healthy people, but can cause stomach and intestinal complaints if resistance is reduced
- Presence of glass, plastic, rubber and other waste
Not only heat and stagnant water contribute to polluted water, but also visitors themselves, says Den Hoed. "Users leave traces in and around the water. For example small children with diapers, people who urinate in the water, pooping dogs or people who feed ducks. All these factors contribute to the growth of bacteria and algae."
What can you do to keep the swimming pool in your area clean?
- Do not let dogs out at swimming pools between May 1 and October 1, to prevent pollution by dog poop
- Do not feed ducklings
- Do not pee in the water, but use the toilet facilities
- Dispose of your waste in the bins or take it back home
- Put on a swimming diaper for small children
Municipalities and water boards can take various measures to improve water quality, for example by mixing diluted hydrogen peroxide with the water to kill the blue-green algae. "But that is actually a patch," says Den Hoed. "It doesn't take away the cause."
The approach at the swimming lake in the Rijswijk Wilhelminapark in 2016 was more rigorous. Then the entire pond was pumped empty, 1,200 kilos of live fish transferred to other water and all the decaying sludge was sucked from the bottom. Finally, the pond was pumped full of clean water.
"But there is not always something to do about the pollution," says Den Hoed. "It's nature. So you can't say," Oh, there's blue-green algae in the water, we're just soaking it up. "It's always a question of whether it works."
If you want to take a refreshing dip in the water, you can check the status of the water in advance on zwemwater.nl. Information about the available facilities and the quality of the water appears here.
See also: 'A stab of the pieterman and your beach day is ruined well'