A storm‐induced suspension interflow (a kind of turbidity current) in subtropical deep (113‐m maximum depth) Feitsui Reservoir, Taiwan, was traced and simulated for both water quantity and quality control. To trace the path of the turbidity current, the spatial and temporal distributions of water temperature, turbidity, and concentration of total phosphorus were obtained weekly from seven sampling sites at 10‐m intervals vertically. These were obtained to trace the path of the turbidity current. A hydrodynamic model simulation agreed closely with the observations. Thermal stratification of the water column was disrupted by storms. After plunging into the reservoir, the suspension interflow resulting from higher concentrations of the suspended solids and lower water temperature moved horizontally toward the dam at depths of 50–60 m. Adjusting the location of subsurface withdrawal accordingly reduced the intake of suspended solids and total phosphorus associated with the turbidity current. Some of the suspended solids in the lower layer might still affect the surface water quality through vertical mixing, especially when thermal stratification is disturbed.