There is swimming advice for the Delftse Hout recreation area as residents are advised not to go into water. Dead birds and fish have been found, linked to illness caused by extreme prolonged heat.
Monday warning signs have been posted in the reclaimed nature area near Delft, which warns of botulism, a poisoning that mainly birds and fish collapse. People can also get health complaints, such as nausea and abdominal complaints.
Bathers are advised not to enter the water and to stay away from dead birds and fish. The bacterium that causes botulism can rapidly multiply in warm and oxygen-poor water. The cadavers found are further investigated.