The Ara River, located in Ara, Southwestern Nigeria, is the largest water body in the area. An ecological assessment of the river was conducted using aquatic insect populations and various environmental factors as indicators to assess its ability to perform crucial ecological and supporting functions. Insects were collected monthly from January to June 2021 using a long-handled D-frame net (500 µm mesh) and hand-picking when needed. Key environmental variables, including water depth, water and air temperature, flow rate, dissolved oxygen (DO), and conductivity, were measured according to standard protocols. A total of 344 aquatic insects were collected, representing 13 genera, 10 families, and 6 orders. Odonata was the most abundant order, with Libellula sp. being the most common species. DO levels were found to be low, while conductivity was elevated. The equitability index indicated a uniform distribution of species across the sampling sites. Analysis of canonical correspondence revealed that several species were closely associated with areas of low dissolved oxygen and high flow rates. The dominance of pollution-tolerant species, along with the low dissolved oxygen and high conductivity, indicates slight pollution in the river at the time of the study. It is essential to address pollution sources to safeguard the river's biodiversity and ensure its continued ecological functionality.
