The Sevre Nantaise River in Vertou, western France, has turned green with duckweed, giving these fishermen the appearance of sailing through a meadow.
Also known as Lemna minuta, duckweed is native to parts of the Americas, and has been introduced into many other countries. Its exact native range is not known.
The plant's distribution has been expanding, and since 2007, it has been spreading in Europe, when it was first reported in Poland. It is considered an unwanted species in many areas, such as Belgium.
However, in other places like the US, duckweed is not considered harmful and is seen to have environmental benefits, such as food for water fowl and shelter for small fish.
Duckweed varies in shape depending on growth conditions. In the shade it is a single green translucent oval body no more than 2.5mm long, and in full sunlight it generally grows in pairs. Under ideal conditions, it can triple its mass in 24 hours.
Duckweed grows in slow-moving, calm, and stagnant freshwater habitats. It requires high temperatures and plenty of sunlight to flourish, and will die out when the temperature gets colder.