Aluminate flocculants are employed widely in water treatment for precipitating suspended solids and emergency treatment of algal blooms in eutrophic lake, but the residual aluminum (Al) may have phytotoxic effects on aquatic organisms after entering aquatic ecosystems. To elucidate the potential impacts of Al on turion germination and early growth in Potamogeton crispus, we conducted a mesocosm experiment using five Al concentrations (0 (control group), 0.3, 0.6, 1.2, and 1.5 mg/L) in alum solutions. The results showed that the germination of turions and the early growth of P. crispus were reduced and inhibited by Al. The maximum numbers of germinating turions and newly-formed seedlings occurred in the control group, and their numbers declined in the end of the experiment as the Al concentration increased. Al at a concentration of 1.5 mg/L decreased the number of germinating turions 3.0 times and the number of newly-formed seedlings 30.7 times compared with the control. The chlorophyll content and root activity decreased when the Al concentration increased. The maximum soluble protein contents in seedling tissues (1.953 mg/g fresh weight) occurred in the 0.6 mg/L treatment group, which differed significantly from the other treatment groups. The Al contents in the seedling tissues had a significant positive correlation with the Al treatment concentrations (P < 0.05, r = 0.763), but negative correlations with the biomass, root number, stem weight, soluble protein, and root activity (r = -0.935, -0.975, -0.907, -0.721, -0.944, respectively). Persistent Al concentration 1.2 mg/L significantly decreased the germination of turions and seedling growth in P. crisp us. These results may facilitate the restoration of aquatic macrophytes and ecological risk assessments in Al-exposed lakes.