Assessment of Water Hyacinth Infestation and Its Ecological Impact on Fisheries in Anambra River, Anambra State

Water hyacinth infestations in Nigerian rivers and lakes have been identified as a significant threat to artisanal fisheries, navigational access, and aquatic biodiversity. This study assesses the extent of water hyacinth (Eichhornia crassipes) infestation, its physicochemical effects on water quality, and its perceived impact on fisheries in a 35-kilometre stretch of the Anambra River in Anambra State, South East Nigeria. Remote sensing imagery was used to estimate spatial coverage of water hyacinth mats, and field sampling was conducted at infested and non-infested stations for dissolved oxygen, pH, temperature, transparency, and nutrient concentrations. Fish sampling was conducted using standardised gill nets at matched infested and non-infested sections. Fisher perceptions were documented through structured interviews with 65 active fishers. Results showed that water hyacinth covered an estimated 28% of the surveyed river stretch. Dissolved oxygen concentrations beneath dense mats averaged 2.3 mg/L, below the survival threshold for many commercially important fish species. Fish species richness was 43% lower at heavily infested stations. Fishers universally reported declined catches and obstructed access to traditional fishing grounds. The study provides ecological and socioeconomic evidence of the damage caused by water hyacinth infestation to the Anambra River fishery and recommends a coordinated mechanical and biological control programme led by the Anambra State Ministry of Environment and Natural Resources.

Keywords: water hyacinth, Eichhornia crassipes, Anambra River, fisheries impact, dissolved oxygen