The twenty-third edition of the Weiswampach triathlon was scheduled for 18 to 19 August. On Monday the Luxembourg water authority issued a safety warning that tests had found early stage cyanobacteria, also known as blue algae, in the lake.

The discovery of the potentially toxic species prompted an immediate ban on bathing and fishing in the lake. On Thursday, the triathlon organisers announced the downgrade of the race series. “Because of the great heat in the last weeks, there is cyanobacteria in the lake and swimming is forbidden right now. Too bad. Of course we have a plan b,” they posted on their Facebook page.

The algae blooms have become an annual occurrence in Lac de la Haute-Sûre, a lake in the centre of Luxembourg which is popular for water sports. But, normally they do not occur until September. The Luxembourg water authority issued a bathing and fishing ban in the latter on 25 July, the earliest yet. The last remaining outdoor bathing spot, in Remerschen, has not yet been impacted by the blue algae.