The purpose of this study is to propose a prevention measure against algal abnormal proliferation in a scenic effluent channel of a wastewater treatment plant in Kobe, Japan. We conducted field work on water quality and algal identification for clarifying the cause of the algal abnormal proliferation and laboratory experiments for demonstrating the inhibiting efficacy of algal growth by NaOCl and seawater. As the results of the field work, it found that main alga in the channel is Fragilaria neoproducta and that the algal abnormal proliferation is caused by features of water quality and structures in the channel. And as a result of the laboratory experiments, it found that NaOCl has the strong inhibition effect of algal growth but also affects growth of Porphyra seaweed in discharged area from the channel. In addition, the result of the experiments demonstrated that seawater does not have the strong inhibition effect of algal growth but has the distributing efficacy of the alga forming colony.