We quantified presumptive extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella, Enterobacter, Serratia, and Citrobacter group colonies from wastewater in Basel, Switzerland, across 3 years to represent before, during, and after the COVID-19 pandemic. Wastewater surveillance might be a noninvasive, sensitive, rapid, and cost-effective instrument for early detection and monitoring local epidemiology.