After hottest summer, weeds turn historic Belgian canals green

A bright green film carpets the historic canals in the medieval Belgian town of Ghent, as tourists and students relax along its edges in the unseasonable autumn warmth.
The blanket of duckweed covering the water has proliferated dramatically due to a lack of rain and record-breaking temperatures, transforming parts of the city’s waterways into vivid expanses of green.
Like much of Europe, Belgium in recent months has experienced an exceptional series of heatwaves, with the summer of 2026 declared the hottest in the country’s history. The unusually warm conditions have continued into autumn, creating an environment in which the normally modest aquatic plant has spread at an extraordinary rate.
“We’ve never seen anything like this here in Ghent”, Davide Siddi, who captains a boat giving tours of the canal, said. “It’s been like this for three weeks to a month”.
The lack of rainfall, coupled with unusually warm weather, with temperatures in September still regularly exceeding 20 degrees Celsius, has provided ideal conditions for duckweed to flourish.
“Normally, the plant is found where water is stagnant, but at the moment it is spreading everywhere”, Geert Weymeis, head of Flanders Waterways, said. “This is the first time we have seen it grow on such a massive scale here”.
Weymeis said the phenomenon mainly affects the Lys, a river that flows from northern France and empties into the Scheldt, which runs through Ghent’s centuries-old canals. The extensive growth has created a striking contrast with the city’s historic architecture, including its churches, medieval buildings and waterways that normally draw visitors for their reflections and clear views of the water.
“It could last for a few more weeks if the temperature does not drop significantly”, Weymeis said.
Although duckweed is harmless to humans and tourists can still safely board the boats that wind their way through the city centre, its rapid growth can affect the aquatic ecosystem. The plant forms a dense layer on the surface of the water, reducing the amount of sunlight reaching flora and fauna beneath it.
Against the blue sky, the pea-green coating creates an unusual scene, prompting passersby to stop and photograph the canals. Yet the striking appearance has also raised concerns about the effects of prolonged heat and changing weather patterns on local waterways.
“It’s both beautiful to look at and a cause for concern”, Ramzi Salhi said after capturing the image.
For boat owners like Siddi, however, the problem is more immediate and practical. The thick layer of duckweed can clog the engines of tourist boats operating on the canals, causing them to overheat and disrupting tours.
“Over the past month, a few boats have already broken down”, he said. — AFP