In Belgium, a thick layer of green duckweed now covers canals in Ghent's historic centre, turning the water into a bright green carpet.

Tour boats continue to operate, but the growth has caused problems: one vessel's motor overheated after duckweed clogged its intake.

Geert Weymeis, spokesperson for the Flemish waterways management body, says the spread is unprecedented, linking it to drought, high temperatures and slow-moving water, which created ideal conditions for the plant.

Students watching from the banks describe the scene as striking, but say it also raises concerns about climate change.