Swimming Prohibited at Rommwiss Beach After Blue Algae Detected

On Thursday 10 September 2026, Luxembourg’s Water Management Agency reported that a proliferation of cyanobacteria, commonly known as “blue-green algae”, has been detected at Rommwiss beach on the Upper Sûre Lake.

According to the agency, as part of the regular monitoring of bathing water quality, analyses carried out on Wednesday 9 September revealed the presence of Microcystis aeruginosa, a toxic cyanobacterium. The toxin concentrations measured also exceed the action threshold.

The agency has advised that due to the health risks, swimming is prohibited with immediate effect at Rommwiss beach, in accordance with the amended Grand-Ducal Regulation of 19 May 2009 concerning special protection measures and monitoring programmes for bathing water quality.

Certain species of cyanobacteria produce toxins that can pose health risks to humans, aquatic wildlife, domestic animals and livestock. For this reason, the Luxembourg Institute of Science and Technology (LIST) has been tasked with monitoring cyanobacterial proliferation in official bathing areas. Cyanobacterial blooms were observed during monitoring on 9 September 2026 (see the national cyanobacteria alert map).

Problems caused by contact with, swallowing, or inhaling these substances vary in nature and severity and may include, for example, headaches, skin irritation and/or burning, and nausea. If you experience health problems after swimming, please consult your doctor and mention any possible contact with toxic cyanobacteria.

For bodies of water where significant cyanobacterial proliferation has been detected, the Water Management Agency, based on advice from the Health Directorate, also recommends that the public:

• Do not allow dogs or other domestic animals to drink the water.

• Avoid any contact with the water.

• Avoid water-based activities (e.g. water sports and fishing).

In particular, when fishing:

• Avoid contact with fish.

• Do not eat fish that have been caught.

• Stop fishing if visible cyanobacterial blooms are present.

Any sighting of blue-green algae in the Grand Duchy of 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.

As of today, swimming remains permitted at the other beaches on Upper Sûre Lake: Burfelt, Fuussefeld, Insenborn, Liefrange and Lultzhausen.

It should be emphasised that there is no risk associated with drinking water supplied from Upper Sûre Lake. This is because raw water is extracted from a depth of 25 m at the dam in Esch-sur-Sûre, where the concentration of cyanobacteria is very low. In addition, the existing water-treatment system can effectively remove toxins produced by cyanobacteria.

The current status of whether official bathing sites are open or closed can be followed on the Water Management Agency’s website: waasser.lu.