Cheung Ek Lake is the biggest wastewater lake inside Phnom Penh City and has massive water and nutrient inflow. Around 70 % of rain runoff and wastewater in Phnom Penh flows into Cheung Ek Lake through three main canals: Trabek Canal, Stung Meanchey Canal, and Lou Pram Canal, before discharging into the Bassac River. Since 2008, the rapid urbanization of the satellite city in Phnom Penh has decreased the area of the lake and contributed to the degradation of the lake's water quality. Cheung Ek Lake performs many functions such as flood control, natural wastewater treatment, and provision of water for vegetable production. Previous studies identified the positive and negative impact of lake water on the local ecosystem and human livelihoods. The aim of the current study was to monitor seasonal changes in water quality in Cheung Ek Lake, Cambodia. Additionally, the objectives of this study were to (i) analyze the changes in water quality parameters in the rainy season and the dry season and (ii) describe daily and hourly changes in phosphate (PO43-) concentration in the lake. For that, selected chemical parameters such as pH, electroconductivity (EC), phosphate, nitrate (NO3-), iron (Fe2+), and dissolved oxygen (DO) were measured in the rainy and dry seasons. In addition, phosphate (PO43-) was analyzed hourly for a week in the dry season. The water samples were collected at 3 points: inlet, middle, and outlet of the lake, at a depth of 0.5 m. Water samples were analyzed in situ using a spectrophotometer. The decreased values of EC, NO3-, PO43-, and Fe2+ from inlet to outlet show that the lake has the potential to reduce the nutrient level in both seasons. Phosphate increases at 10 am, 1 pm, and 7 pm indicated that water quality was remarkably affected by daily rush hours of household activities. This further suggested that household activities could be the main sources of the presence of a high concentration of PO43- in the lake.