Belgium Hits Record 62 Swimming Bans From Blue-Green Algae
Belgium has imposed 62 temporary swimming bans across 49 different open-water locations this summer, all caused by outbreaks of blue-green algae. The figure already surpasses the 58 temporary bans recorded during the entire previous summer, which was itself a record, according to VRT NWS.
Blue-green algae, or cyanobacteria, are toxic bacteria that can cause skin rashes, stomach and intestinal complaints, and in extreme cases damage to the liver, kidneys, and nervous system. Their presence in swimming zones has forced authorities across Flanders to close numerous popular spots, from the Damse Vaart in Brugge to the IJsevijver in Overijse and the Keerdok in Mechelen.
Why Blue-Green Algae Are Thriving
The unprecedented number of bans is directly linked to this summer’s extreme weather conditions. Michiel Verhamme of the Vlaamse Milieumaatschappij (VMM), the Flemish Environment Agency, explained the phenomenon in an interview with VRT NWS: “Blue-green algae thrive especially well in shallow and stagnant water. And the drought and heat are precisely what cause there to be little water at many locations, where they can grow very quickly and intensely.”
Blue-green algae are actually not algae at all, but cyanobacteria - bacteria that look like algae and perform photosynthesis. According to Veerle Van Woensel, also of the VMM, the bacteria become dangerous when they form a floating layer on the water’s surface. “Most blue-green algae are actually toxic to humans and animals,” she said.
Climate change is compounding the problem. “Warm, dry periods and climate warming cause blue-green algae to occur more often and earlier in the year,” Van Woensel noted. “The average water temperature of swimming and recreational ponds during the bathing season shows a rising trend.”
The Broader Drought Crisis
The algae blooms are unfolding against the backdrop of one of Belgium’s most severe droughts on record. Minister Jo Brouns (CD&V) has called on Flemish residents to be extremely economical with water, warning that the drought becomes more visible every day. Approximately 83 percent of groundwater measurement points are recording low to extremely low levels for this time of year, with nearly half showing exceptionally low values, according to the VRT NWS drought liveblog.
A third heatwave is currently underway, with temperatures reaching 32.2 degrees Celsius in Ukkel on August 13 - a new daily record. The combination of heat and drought has created ideal conditions for cyanobacteria to multiply rapidly in shallow, slow-moving water bodies.
Affected Locations Across Flanders
Swimming bans have been imposed at locations across the country. In Brugge, a 900-meter stretch of the Damse Vaart was closed on June 26 after a floating layer of blue-green algae was detected. Mayor Dirk De fauw said the city was taking no risks with swimmers’ health, as reported by VRT NWS.
The IJsevijver in Overijse was closed on July 1 after routine water quality checks detected the bacteria. Alderman Leo Van den Wijngaert acknowledged the disappointment for swimmers but stressed that safety came first: “Given the safety risk, it cannot be otherwise,” he said, according to VRT NWS.
The Keerdok swimming zone in Mechelen was also temporarily closed after measurements on July 24 confirmed the presence of cyanobacteria, as documented on the official water quality monitoring site.
More recently, the recreation area De Mosten in Hoogstraten was closed on August 12. The municipality is attempting to accelerate recovery by pumping extra water into the pond, VRT NWS reported. The city of Gent also postponed the opening of three temporary public swimming zones at Keizerpark, Portus Ganda, and Houtdok indefinitely due to persistent algae blooms, according to VRT NWS.
A Growing Trend
The number of swimming bans has been steadily increasing over the past decade. In 2024, 23 bans were recorded by early August - already a record for the first half of the year at that time, as reported by Plus Magazine. Last year saw 58 bans, and this year has already surpassed that total with 62.
Most bans last only a few days before conditions improve. As Verhamme explained, rain can help dilute the algae and restore oxygen levels. “Blue-green algae can bloom very quickly, but also disappear quickly,” he said. “It helps when it rains, then more water comes and it gets somewhat diluted.”
Policy Implications
The algae crisis comes at a pivotal moment for Flemish water policy. Minister Brouns has decided that from June 1, 2027, swimming in open water will be allowed everywhere in Flanders unless explicitly prohibited - a reversal of the current rule that swimming is banned by default. The policy aims to create approximately 140 additional swimming locations, as reported by VRT NWS.
The new approach places greater responsibility on water managers and swimmers themselves. However, the current algae outbreaks highlight the challenges ahead: as more swimming locations open, water quality monitoring and management will become even more critical.
What to Watch For
With the third heatwave of the summer still underway and no significant rainfall forecast in the immediate term, additional swimming bans are likely in the coming weeks. The VMM and local authorities will continue monitoring water quality at affected locations, with most bans expected to lift once temperatures cool and rain returns. The long-term question remains whether climate warming will make blue-green algae blooms a permanent summer fixture in Belgian waters - and what that means for the country’s ambitious plans to expand open-water swimming.