Operation of conventional drinking water treatment plants (DWTPs) is limited by seasonal variations in the characteristics of raw water, such as algae levels and turbidity. In this study, an integrated flotation and sedimentation unit (IFSU) with side flow-inclined plate settlers (SFIPS) was applied to enhance the removal ratio of algae and turbidity in a full-scale field experiment. To accomplish this, the performance of two IFSU reactors (with and without SFIPS) treating algal-rich water, low-turbidity water and high-turbidity water was compared. Extensive experiments were conducted based on a central composite face-centered design, and the results were analyzed using response surface methodology. Polyaluminium chloride dose, NaOH dose, influent turbidity level and influent chlorophyll level were selected as the operating variables to analyze, optimize and model the process. The results showed that SFIPS functioned as a counterflow inducer to enhance the effects of stratified flow patterns and decrease the clarification loading rate in the separation zone during the dissolved air flotation process, leading to considerable increases in algae and turbidity removal in the IFSU reactor. The results of this study will facilitate upgrades of conventional DWTPs to improve their potential.