"Sorry, no data ..."
Brussels region is made of more then 2% (350000 m2) lakes. 25 of them are big enough to be considered swimmable. 12 of those are significantly bigger than the Boekenberg swimming pond (2775m2) in Antwerp, the Belgian reference for swimming ponds. If Brussels had 25 swimmable areas it would allow Bruxelloisans (1,139 million people) to swim in more open air swimming area's than all Londoners and Parisians combined (10,784 million people).
The reality is different. We received the information that there is no data available about the biological water quality regarding swimming since the Brussels Region isn't monitoring the relevant parameters at all. Instead they simply assume that the water quality is either too bad for swimming, or that swimming would harm the natural ecosystems. Based on these assumption there are not plans to install a public swimming facility on the existing waters in the near future.
When you read between the lines, it's clear that one underlying reason for not collecting the necessary data is the fear that swimming spots will only create trouble because of the shear pressure on such a place. That's not an appropriate strategy. In fact, it's no strategy at all.