Warning for blue-green algae in warming waters; Record streak of summer days in June

Rijkswaterstaat, provinces, and water boards warn bathers about blue-green algae. This disease-causing bacterium grows rapidly when the water in ponds and lakes warms up. Water temperatures have risen sharply in recent days due to the continued warmth, while water levels are dropping due to evaporation. Dog owners should also not simply let their pets jump into ponds or other municipal waters, water authorities emphasized.

The heat is the result of the series of warm days in the Netherlands. For instance, a record streak of summery June days have been measured in De Bilt. On Saturday, the temperatures rose to 25 degrees at 1 p.m., making it the ninth summer day in a row in De Bilt, Weeronline reported. The previous record was eight summery June days in a row, dating back to 1976. The warmest day in this year's series was Sunday, June 11, with 30.3 degrees, the only tropical day in the Netherlands. The weather service predicts that the record series will be even longer, with a tenth summer day on Sunday. Then it will be 29 to 30 degrees in De Bilt.

Gelderland has already placed warning signs at several swimming pools in Achterhoek and near the Veluwe. Waterschap Delfland, which includes Rotterdam and The Hague, warns of blue-green algae in swimming pools at Delftse Hout, Wollebrand, and Krabbeplas, among others. For the lake in Madesteijn, there is even a swimming notice advising against swimming in the lake. The Vechtstromen water board in Twente and part of Drenthe has also detected blue-green algae. In addition, Scheldestromen in Zeeland advises against swimming in ponds that “do not smell fresh”.

The blue-green algae is a bacterium that forms a floating layer in warm water. This floating layer produces toxins that can make people and animals very sick. As the weather continues to be very warm, other diseases are appearing in open bathing waters, such as the harmless but very troublesome swimmer's eczema. Botulism, however, has not yet been reported. This disease, which kills ducks and fish, thrives in continued heat. If, as expected, it rains on Sunday or Monday, the water in ponds and lakes will cool down and the infections will disappear again.

During the swimming season, the water authorities check hundreds of places with natural water throughout the country. You can see where it is safe to swim at www.zwemwater.nl.