ASSESSING THE MACROBENTHIC ORGANISMS AS BIOINDICATORS IN THE ETHIOPE RIVER ALONG THE AXIS OF SAPELE, DELTA STATE.ASSESSING THE MACROBENTHIC ORGANISMS AS BIOINDICATORS IN THE ETHIOPE RIVER ALONG THE AXIS OF SAPELE, DELTA STATE.

ABSTRACT This study assessed the physicochemical characteristics and macrobenthic community structure of the Ethiope River along the Sapele axis, Delta State, Nigeria, from March to June 2025, to determine the influence of anthropogenic activities on aquatic ecosystem health. Three stations were investigated: Station 1 (Efurokpe, abattoir discharge zone), Station 2 (Jamieson, sawmill zone), and Station 3 (Michaga/Ojolu canal, urban runoff zone). Significant spatial differences (p < 0.05) were observed for pH, flow velocity, dissolved oxygen (DO), biochemical oxygen demand (BOD), transparency, and total dissolved solids (TDS). Station 2 displayed the most favorable conditions, with near-neutral pH (6.85), highest DO (5.65 mg/L), lowest BOD (3.73 mg/L), and minimal TDS (58.75 ppm), supporting the highest benthic abundance (371 individuals) and diversity (Shannon index: 2.71). Gastropods such as Typanotonus spp. and Cerithidea spp. were dominant here. Station 1 showed moderate quality, with 289 individuals (Shannon index: 2.40) and elevated BOD (6.22 mg/L). Station 3 was the most polluted, with the lowest DO (3.38 mg/L), highest BOD (7.70 mg/L) and TDS (90 ppm), and reduced benthic abundance (193 individuals, Shannon index: 2.50). This station was dominated by pollution- tolerant taxa, while sensitive species were scarce. The results highlight strong correlations between pollution gradients and benthic distribution, confirming macroinvertebrates as effective bioindicators. Targeted management is required to reduce organic load, particularly in the highly impacted urban runoff zone (Station 3).