Acid extracts from leaves and roots of Eichhornia crassipes (water hyacinth) were tested as corrosion inhibitors for mild steel in hydrochloric acid solutions using a gasometric technique. The effects of temperature and concentration on the inhibition performance of the extracts have been studied. The results show that both the leaf and root extracts functioned as effective corrosion inhibitors, with the leaf extracts exerting a greater effect. Fitting of the experimental data to the Arrhenius and transition state equations revealed that the organic constituents of the extracts were physically adsorbed on the corroding mild steel surface. The adsorption characteristics of selected extract constituents were theoretically evaluated by molecular dynamics simulations in the framework of the density functional theory and confirm distinct adsorption of the extract organic matter on the mild steel surface. Our findings provide ready eco-friendly application for the problematic fresh water weed Eichhornia crassipes.