The Amagasaki Canal, an enclosed waters, have been polluted and eutrophication and hypoxic condition occurr chronically. To restore the aqueous environment of the canal,a water purifying plant was designed and substantiative experiment have been conducted by Amagasaki Sea Blue Project. The water improvement cannel using algae part of the plant is highly effective in improving desolved oxygen and importing nutrient in day time. However, desolved oxygen consumption and nutrient release are caused by the decomposition of dead algae during night time. To solve the problem, exciation of photosynthesis by LED light is devised. In this study, the effect of productivity and nutrients importation by LED light irradiation was evaluated, and application methodology of LED light such as installation span and photon density were estimated.