The Ministry of Health has issued a warning that people should avoid swimming in areas of the Moselle where blue algae can be seen.
Blue algae or cyanobacteria has been found in areas of the Moselle river.
The algae can cause skin irritations, headaches, nausea, cramps, and liver damage.
Especially in more stagnant parts of the river, elevated levels of blue algae have been measured.
Cyanobateria poses a risk to humans and animals alike, which is why direct contact with water from the Moselle river is not recommended.
Areas affected by blue algae can be recognised as they form green 'carpets' in the water. Swimming and other water sports should be avoided.
Last year, the Haute-Sûre lake was especially affected by blue algae, with the Water Management Agency issuing swimming bans at one of Luxembourg's most popular lakes.