The semi-arid nation of South Africa deals with critical water shortages and deteriorating water quality because of rising population numbers as well as expanding urban areas and industrial operations. The protection of water resources depends heavily on wastewater treatment, yet treated wastewater continues to serve as a significant pollution source. The study assesses environmental effects from the Atlantis (Wesfleur) Wastewater Treatment Works (WWTW) located in the Western Cape while studying its pollution impact on the Donkergat River. The research team obtained water samples from the treatment plant effluent and river water downstream between October and November 2023 to measure COD, TSS, nitrates, orthophosphates, chloride, conductivity, sulphates, and pH levels. The Atlantis WWTW effluent met all requirements set by the Department of Water and Sanitation (DWS) and South African National Standards (SANS 241-1:2015). The COD, TSS, and nutrient measurements in the treated water stayed within the established limits. The river water quality showed high chloride (264 mg/L) and sulphate (1543 mg/L) levels during multiple sampling events because of wastewater discharge accumulation and suspected human-made pollution sources. The WWTW achieves satisfactory treatment performance, but the research demonstrates that ongoing surveillance, facility enhancements, and environmental protection strategies are essential to protect water bodies. The results support the ongoing discussion about achieving proper wastewater treatment and environmental protection in areas with limited water resources.