Monthly sampling was conducted for a period of 24 months (January 2022–December 2023) at three locations—Kalgwai, Dingare, and Marke—within Kalgwai Reservoir to examine variations in selected physicochemical properties of the water. The parameters assessed comprised temperature, transparency, hydrogen ion concentration (pH), dissolved oxygen (DO), alkalinity, ammonia, and hardness, measured using established field techniques following Dauda and Akinwole (2014) and APHA (2012). Data generated from the study were subjected to descriptive statistical analysis, analysis of variance (ANOVA), and t-test procedures. The findings indicated pronounced spatial and temporal variability in most of the measured parameters. Significant differences (P < 0.05) were observed across stations and months for temperature, pH, dissolved oxygen, alkalinity, and hardness. Seasonal variation was significant for temperature, dissolved oxygen, and hardness, whereas transparency, pH, alkalinity, and ammonia did not vary significantly between seasons. The results reflect the dynamic physicochemical conditions of Kalgwai Reservoir and provide essential baseline information for effective water quality monitoring and management.