In this paper, we analyzed a mathematical model of algal-grazer  dynamics, including the effect of colony formation, which is an example of phenotypic plasticity. The model consists of three variables, which  correspond to the biomasses of unicellular algae, colonial algae, and  herbivorous zooplankton. Among these organisms, colonial algae are the  main components of algal blooms. This aquatic system has two stable  attractors, which can be identified as a zooplankton-dominated (ZD)  state and an algal-dominated (AD) state, respectively. Assuming that the  handling time of zooplankton on colonial algae increases with the colonial  algae biomass, we discovered that bistability can occur within the model  system. The applicability of alternative stable states in algae-grazer dynamics as a framework for explaining the algal blooms in real lake ecosystems, thus, seems to depend on whether the assumption mentioned above is met in natural circumstances.