Assessment of Industrial Pollution Impacts on Freshwater Fish Biodiversity in the Warri River, Delta State

This study assesses the impact of industrial effluent discharges on freshwater fish biodiversity in the Warri River, Delta State, South South Nigeria. The Warri River receives effluents from petroleum refineries, petrochemical facilities, and industrial estates in Warri municipality, and the cumulative effects of these discharges on fish community structure have not been fully characterised at the upstream-to-downstream gradient. Fish sampling was conducted at eight stations along a 45-kilometre river reach from an upstream reference station to stations progressively closer to and downstream of industrial discharge points, using electrofishing and gillnet sampling during wet and dry seasons. Simultaneously, water quality parameters including dissolved oxygen, pH, conductivity, temperature, and total petroleum hydrocarbon concentrations were measured at each station. Fish community composition was analysed using species richness, diversity indices, and biotic integrity metrics. Results show a progressive decline in fish species richness and diversity from the upstream reference station towards the industrial discharge zone, with species richness declining from 28 species at the reference station to nine species at the most heavily impacted downstream station. Dissolved oxygen depletion below 3 milligrams per litre is recorded at three heavily impacted stations. Pollution-tolerant species including catfish become dominant in the impacted zone, displacing sensitive species. Total petroleum hydrocarbons exceed guideline values at five stations. The study concludes that industrial effluent discharge has fundamentally altered fish community structure. Recommendations include mandatory effluent treatment upgrades and real-time discharge monitoring at major industrial outlets. Keywords: fish biodiversity, industrial pollution, Warri River, Delta State, water quality.