Sh*t smell in the city center. Literally.

I've been smelling some weird stuff (literally smells like sewage) all along the Ernest Van Dijckkaai and Grote Marks area, it comes mostly in the afternoons/evenings. And it STAYS. For hours. Some friends said it's because of the new work by Schelde in the Zuid, that the municipality plants new trees and that's the smell of the fertilizers. But I really suspect something is being sprayed to the air on top of the whole city. Anybody else noticed a constant weird smell in the center lately?