Cypermethrin is a synthetic pyrethroid insecticide widely used in agriculture, industry, and domestic applications. It is highly toxic to aquatic organisms and subject to a stringent Environmental Quality Standard of 0.00008 μg/L in freshwater. In anticipation of new discharge permits, a two-year monitoring programme was conducted across 43 Wastewater Treatment Works to assess cypermethrin occurrence and removal. Over 4,500 samples of influent, effluent, and receiving waters were analysed. Results showed that activated sludge processes achieved greater removal compared to biological filtration, while chemical dosing had negligible impact. Granular Activated Carbon demonstrated effective removal in column tests across four media types, highlighting its potential as a quaternary treatment option. These findings provide critical evidence to support compliance with future permits and inform strategies for tackling cypermethrin and other emerging micropollutants in wastewater.