The length–weight relationship (LWR) and relative condition factor (Kn) of Cyprinus carpio from the Ottu Reservoir in Sirsa, Haryana, India, were studied in order to assess the species growth pattern and its physiological condition within the reservoir ecosystem. Using various fishing gear, fish samples (n = 260) have been collected from four sampling locations between January 2025 to December 2025. The body weight (g) and total length (cm) have been measured and evaluated using the cube law equation, W=aLb. Both sexes' length and weight were strongly correlated, with high coefficients of determination (R2 = 0.96) in the length-weight relationship. The female C. carpio showed positive allometric growth (b = 3.1605), indicating relatively larger weight gain relative to length, probably related to gonadal development, whereas males showed near-isometric growth (b = 2.9833), indicating proportional rise in weight with length. For both males (1.0055) and females (1.0192), the mean relative condition factor (Kn) was close to unity, reflecting generally good physiological condition and favourable conditions in the reservoir. There were seasonal differences in Kn, with relatively larger values in the spring and summer, possibly as a result of greater food availability and reproductive activity and slightly lower values in autumn and winter. Overall, the results reveal that C. carpio populations in the Ottu Reservoir maintain constant growth and a good condition of health, underscoring the reservoir's suitability and highlighting the significance of continuous monitoring for sustainable fisheries management and conservation.