This segment of river is called "Zwalm" but that should be "Zwalmbeek", just like the segments before and after.
I noticed this anomaly on https://waterwaymap.org/river/Zwalm%20001442439176/ where Zwalmbeek is both a tributary and an outflow of Zwalm because of the inconsistent naming. (The reason is probably that Zwalmbeek is often called "Zwalm" by locals, but Zwalmbeek is the official name.)
I hesitate to edit this myself because there's also a tunnel involved (the river goes through the tunnel) under the road - I suppose that should be a separate feature?