Improper disposal of wastes as an environmental problem is common in African and other developing countries of the world, and it raises concerns due to its potential threats to the life of organisms in both terrestrial and aquatic ecosystems. In this study, Asa River in Ilorin, Nigeria was evaluated for cytogenotoxicity at 25.0 %, 50.0 %, 100.0 % following the Allium cepa assay. Water samples were collected from three points tagged A, B, C, and each point was 500 m apart from each other. The water samples were used to grow A . cepa for microscopic and macroscopic toxicities screenings. Heavy metals and volatile organic pollutants in the water were elucidated following the Atomic Absorption Spectroscopy and Gas Chromatography-Mass Spectroscopy. The Water samples induced higher mitotic index values, except the sample C which induced smaller mitotic index value than the negative control. Root growth in the exposed A . cepa was significantly promoted at 25.0 % of the water samples, while significant reduction was obtained at 50.0 % and 100.0 % of the sample C, and 100.0 % of the sample A. The absolute water sample A induced highest percentage chromosomal aberrations, as the water samples B and C induced higher percentage chromosomal aberration than the negative control. Cadmium was detected at a concentration higher than its permissible limit in drinking water unlike Zinc, Iron, Manganase. Poly aromatic hydrocarbons, Aromatic amines, Acridine dye, Phenolic and Polychlorinated compounds were detected in the water sample. These pollutants may be responsible for the observed proliferative, inhibitory, cytotoxic and genotoxic effects of the water samples on A . cepa cells. Our results suggest that Asa River is polluted, having potential to inflict different adverse effects on human, animals and plants utilizing it along its course.