Textile dye effluents pose a severe threat to environmental and public health in Algeria, necessitating sustainable remediation strategies. This study explores the application of cesium-substituted Dawson heteropoly acid (HPA) photocatalysts for solar-light-driven degradation of dye pollutants like methyl blue in water as an eco-friendly treatment approach. Cesium-substituted Dawson HPAs were synthesized and systematically evaluated for photocatalytic decolorization of methyl blue under direct sunlight irradiation. Critical parameters, including catalyst dosage, dye concentration, H₂O₂ levels, and the influence of inorganic ions (chloride, nitrate, and sulfate), were investigated at neutral pH. The optimal conditions of 1 g/L catalyst, 10 mg/L dye loading, and 3.92 mM H₂O₂ concentration were established to achieve nearly complete decolorization (DE=98%) within 90 minutes. Sulfate ions specifically inhibited dye decomposition, presumably due to scavenging effects. The synthesized cesium-HPA exhibited excellent solar photocatalytic activity for treating dyestuff effluents. Further research should focus on optimizing catalyst design, elucidating mechanisms, and scaling up this technology for practical industrial applications to facilitate the ecological restoration of water bodies impacted by textile effluents. Widespread adoption of such clean catalytic processes can raise awareness about mitigating the dangers textile dyes pose to the environment and ecosystems. Collaborative efforts between academic institutions, industry, and governmental agencies are recommended to develop integrated solutions leveraging this polyoxometalate photocatalysis platform for environmental remediation and to disseminate these research results concerning ecological restoration.