Water bodies in cities often suffer from intense eutrophication due to excessive nutrient addition. Hence, the restoration of a eutrophic water body to its original healthy state is crucial. Therefore, this research investigated the possible use of polyaluminium chloride (PAC) to restore a shallow pool in Thailand. A dosage of PAC at 30 g/m² was applied as slurry in a shallow pool in 2021. Water quality and sediment properties were monitored before, during, and after the application of PAC (four consecutive weeks). The results revealed that before the application of PAC, this shallow pool was hypereutrophic (mean total nitrogen of 0.74±0.32 and mean total phosphorus of 3.24±0.88 mg/l). Mean chlorophyll a was exceptionally high (887.45±48.33 μg/l). The predominant species were Spirulina sp. and Microcystis sp. After the application of PAC, the water quality parameters improved. The total phosphorus, chlorophyll a and turbidity were reduced significantly (p<0.05), and the transparency depth was enhanced. Furthermore, intact phytoplankton cells were shifted from cyanobacteria to green algae. Flocs were observed in the surface water and on the sediment. This method proved to be practical to use, low in operational cost, and did not affect freshwater fauna due to its low toxicity.