Ecological Status of Freshwater Macroinvertebrates in Anambra River, Anambra State

Freshwater macroinvertebrates are widely used as bioindicators of river ecological status due to their sensitivity to pollution, well-known taxonomy, and sedentary life histories. This study evaluates the ecological status of macroinvertebrate communities in the Anambra River, Anambra State, South East Nigeria, a major tributary of the Niger River that flows through agricultural and urban catchments. Benthic macroinvertebrates are sampled quarterly in 2024 using a Surber sampler at eight stations spanning a 60-kilometre river reach from Ogbaru to Ayamelum local government areas. Organisms are preserved in 70 percent alcohol, identified to family level, and counted. The EPT richness index (Ephemeroptera, Plecoptera, Trichoptera), BMWP score, and ASPT are computed as ecological status metrics. Concurrent measurement of physicochemical parameters including dissolved oxygen, pH, total dissolved solids, conductivity, and nutrient concentrations establishes the environmental context. Percentage organic matter and grain size of collected substratum are determined for habitat characterisation. Ordination analysis (Non-metric Multidimensional Scaling) is used to identify community assemblage patterns and relate them to environmental gradients. Results are expected to indicate good to moderate ecological status in upstream reference sections and poor status in agricultural runoff receiving reaches. Reduction in EPT taxa and dominance of Diptera larvae characterise impacted stations. The study informs riparian zone management plans for the Anambra State Ministry of Lands and Water Resources. Keywords: macroinvertebrates, Anambra River, biotic index, ecological status, river health