Abstract: The effects of HgCl_2on lake ecosystems in different seasons were studied by investigating the influence of HgCl_2with different concentrations on the growth of two algal species and their adsorption capacities to HgCl₂. The two species, Navicula and Microcystis wesenbergii, have growth advantages in winter and summer, respectively. The results showed that Navicula was more sensitive than Microcystis wesenbergii to the mercury exposure. When the concentration of HgCl₂ was in the range of 1×10^-9-1×10^-7 mol/L, the growth of Microcystis wesenbergii was promoted in low concentrations and inhibited in high concentrations, while the growth of Navicula was inhibited in the whole range and the inhibitory effect was more obvious along with the concentration increase. The adsorption experiments showed that the adsorption rate of Microcystis wesenbergii and Navicula on HgCl_2were in the range of 88.4%-98.8% and 87.1%-97.5%, respectively. Moverover, the adsorption rate and absorption amount of the two species gradually increased with the concentration increases. This demonstrated that both Microcystis wesenbergii and Navicula had strong adsorption effects on HgCl₂, and algae adsorbing mercury from aqueous phase would be harmful to water environment due to their potential mercury accumulations.