Lake ecosystems can be viewed as complex systems where organisms and materials interact in many ways. The features of complex systems are two. One is nonlinear interaction, and another is effect of network formation between organisms and materials. A regime shift is a result of repetition by a chain of both effects. Water level operation of Lake Biwa causes serious concern with an influence on the ecosystem. Concretely, a state shift from turbid water to clear water may occur in response to

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... kness of macrophytes in the Southern Lake Biwa. It would appear that phenomenon of a regime shift occurred. In this paper, we predict a regime shift for the lake. Water quality analysis model is developed under a multi-layered model to predict 2-dimensional property of water quality through a year in the lake. This study illustrates ecological impacts of the water level operation through numerical experiments.