Abstract
<title>Abstract</title> <p> This study evaluated the interconnected dynamics of water physico-chemical parameters and aquatic insects within the Omi River, a perennial lotic system in the Iwajowa Local Government Area of Oyo State, Western Nigeria. Sampling was conducted across five stations over an annual cycle spanning December 2024 to September 2025 to capture seasonal variations. Physico-chemical water properties and hydromorphological variables were monitored alongside an inventory of resident aquatic insect communities. A total of 1,040 individuals belonging to 6 orders, 19 families, and 44 genera were cataloged, exhibiting a strong dominance of <italic>Rhagovelia</italic> sp. (24.04%). Spatial analysis revealed high environmental uniformity across all stations, with biological oxygen demand (BOD) being the only parameter to show significant spatial variation (p < 0.05) due to mild downstream organic enrichment at Station 5. Conversely, the bimodal tropical climate drove sharp seasonal fluctuations. River width, depth, volumetric discharge, turbidity and dissolved oxygen (DO) significantly peaked during the wet season (p < 0.001), while total dissolved solids (TDS) and electrical conductivity (EC) concentrated significantly during the dry season (p < 0.001). Total abundance and diversity metrics peaked in the stable dry season, while individual EPT numbers surged during wet-season aeration. Canonical Correspondence Analysis (CCA) demonstrated that hydromorphological attributes (discharge, depth, stream width, turbidity) were the primary ecological forces structuring species distribution, overwhelming nutrient gradients. The study concluded that, the Omi River retains high biological integrity as at the time this study was conducted, providing a crucial baseline framework for West African freshwater conservation. </p>