Abstract Aquatic insects are regarded as one of the very important components of the freshwater ecosystem because of the various ecological purposes which they serve. The insects are also the most impacted when surface waters are disturbed. As such, analyzing the structure of assemblage has become a veritable yardstick in the assessment of biodiversity and water quality. This research effort applied the combination of aquatic insect composition and physico-chemical characteristics in assessing the ecological status of Oju Awo stream. Aquatic insects and water samples were collected once in every two months covering a period between December, 2021 and October, 2022 using sweep nets and1L sterilized bottle respectively. The results obtained for the physical and chemical parameters of the water as well as the aquatic insect assemblage showed that the investigated reaches of the stream did not differ widely except for water temperature which showed significant variations (p < 0.05) along the reaches of the waterbody. A total of 242 aquatic insect specimens represented by three (3) orders (Hemiptera, Odonata and Coleoptera) and sixteen (16) taxa were recorded. Hemiptera was the dominant and most abundant taxa as it accounted for about 90.91% of the total insect collection. The dominance of pollution tolerant species, the absence of sensitive insects' species and poor water quality as revealed by the physico-chemical parameters indicated deteriorating water quality conditions in the stream. Keywords: Aquatic insects, tropical stream, abundance, diversity, water quality 1 Adeyemi Federal University of Education, Ondo, Nigeria. 2* Obafemi Awolowo University, Ile-Ife Nigeria. NJE Vol. 40 (1): 126-137, 2024 Nigerian Journal of Entomology Published by Entomological Society of Nigeria www.esnjournal.com.ng DOI. Freshwater resources are considered critical in the sustainability of life and maintenance of the balance in nature (Mahmoud, 2020). However, the inadequacy of good quality water has made it imperative to continuously assess the quality of freshwater bodies around the world. This is because most freshwater bodies are becoming deteriorated on a daily basis as a result of the influence of ever increasing anthropogenic activities (Leisher et al., 2022). Furthermore, the Millennium Ecosystem Assessment revealed that many of the freshwater ecosystem species are threatened with extinction and this has been attributed to the impacts of anthropogenic activities and other related effects (Cirella et al., 2019). Many countries around the world are currently confronting the challenge of managing the increasing risks and the consequential effects of temperature change INTRODUCTION and urbanization. More critical is the fact that accessibility to clean water for its intended purposes has become problematic in many parts of the world. In Nigeria, the populace is increasingly finding it extremely difficult to access potable water due to rising volume of anthropogenic activities (Amusan and Balogun, 2019). In fact, most freshwater bodies in the country are polluted while some are gradually drying out due to exposure to pollution and other stress factors (Adenuga et al., 2006). This has led to the reduction in biodiversity, destruction or degradation of the aquatic ecosystem and the life forms there in (Akindele et al., 2014 Aquatic insects also constitute the most diverse and important component of the biota in the freshwater ecosystem and this informs their importance as critical elements in the ecological dynamics of freshwater ecosystems (Folami et al., 2019). Aquatic insects equally *Correspondence email; tundeamusan5@yahoo.com, ORCID NUMBER: 0000-0003-1245-263X Aquatic Insects Diversity and Water Quality of a Tropical Freshwater in Federal University of Education, Ondo, Nigeria 1 2* Adeleke, S.O. and Amusan, B.O. 10.36108/NJE/4202/04.0111