Blue algae at Rommwiss Beach 17 July 2024; Credit: AGE

On Wednesday 31 July 2024, Luxembourg's Water Management Authority announced that blue-green algae has been observed in the upper part of Weiswampach lake, resulting in a swimming ban and the recommendation to avoid all nautical activities for the entire upper lake.

As part of regular monitoring of the quality of bathing water, a significant proliferation of cyanobacteria, also known as "blue algae", was discovered in the entire upper part of Weiswampach lake.

Given the health risks, the authorities have issued a swimming ban with immediate effect for the entire upper part of Weiswampach lake following the 2009 amended Grand Ducal regulation determining special protection measures and monitoring programmes for the state of bathing waters.

The Water Management Authority noted that certain species of cyanobacteria produce toxins which can pose a health risk for humans, aquatic fauna, domestic animals and livestock. As a result, the Luxembourg Institute of Science and Technology (LIST) was mandated to monitor cyanobacteria in bathing water in the Grand Duchy. These analyses on Tuesday 30 July 2024 revealed the presence of species of cyanobacteria potentially producing toxins and therefore potentially harmful to health.

Symptoms of illness linked to contact, ingestion or inhalation of these substances vary in nature and intensity but can for example include headaches, skin irritations and/or burns or nausea. Anyone who experiences health problems after swimming is advised to contact their GP, mentioning possible contact with toxic cyanobacteria.

For water bodies in which a significant proliferation of cyanobacteria has been noted, the Water Management Authority (based on the assessment of the Health Directorate), has recommended that the public:

- do not let dogs or other domestic animals drink the water;
- avoid any contact with the water;
- avoid any water activities (e.g. water sports, fishing).

Especially when fishing, people should:

- avoid contact with fish;
- not consume caught fish;
- abandon fishing activity if cyanobacteria blooms are visible.

Any observation of blue algae in Luxembourg can be reported via the "Bloomin'Algae" app and will be assessed by a LIST expert. All reports can be viewed on cyanowatch.lu.

At present, swimming remains authorised in the lower part of Weiswampach Lake, namely Liefrange, Fuussefeld, Insenborn and Lultzhausen and in the ponds of Weiswampach, Echternach and Remerschen.

The Water Management Authority noted that, in accordance with the provisions of the amended Grand-Ducal Regulation of 19 May 2009, the bathing season will end on 30 September 2024.

The current situation regarding the opening or closure of official bathing sites can be followed on the website of the Water Management Administration: www.waasser.lu.