Although copper is essential for plant growth and development and plays an important role in many physiological processes, excess copper, resulting from industrial development and population expansion in the recent decades, leads to environmental pollution and has been a cause of wide concern for the adverse effects on photosynthesis, metabolism and growth of plants. The growth properties (e.g. fresh weight, root length, height), photosynthetic properties (e.g. gas exchange, chlorophyll a fluorescence, chlorophyll content) and the physiological index (e.g. activity of antioxidant enzymes and osmotic regulators) of Eichhornia crassipes were assessed under various Cu2+ concentrations in hydroponic experiments. The growth of E. crassipes was negatively affected by Cu2+ treatments, especially at higher Cu2+ concentrations; the Cu2+ treatments resulted in decreased photosynthesis because of a decrease in leaf chlorophyll content and damage to PSII functions, except the oxygen‐evolving complex. The physiological tolerance of E. crassipes to Cu2+ relies on osmotic regulation, anti‐lipid peroxidation and improved antioxidant properties. The results indicate that E. crassipes could be considered as a phytoremediation agent for Cu2+ pollution in aquatic environments. However, the benefit of E. crassipes for Cu2+ removal in a highly polluted aquatic environment will be limited, but it will be effective in remediating sites with low pollution (≤5 mg·l−1). The present results could provide not only a basis for understanding the effects of pollutants on photosynthesis in plants under heavy metal stress but also provide a basis for choosing plants for phytoremediation. The photosynthetic rate and growth of E. crassipes is greatly affected by Cu2+ in aquatic cultivation, and the negative effect of Cu2+ on E. crassipes is dose‐dependent, but E. crassipes might adapt to moderate Cu2+ pollution (≤ 5 mg·L‐1) through osmotic regulation, anti‐lipid peroxidation, and the improvement of its antioxidant properties.