To provide a system and a method which can effectively inhibit pollutants such as water blooms from growing in a closed body of water with stagnating water such as lakes and marshes when the water temperature rises in summer, can be inexpensively provided, and can effectively and easily inhibit pollutants from growing.

The system comprises at least one float 2 disposed on the surface part of water held in the closed body of water 1 and forming a passageway 4 in the surface part and a plurality of water flow generation means 3 that are immersed and disposed in the part of the surface part which is spaced from the float 2 and generate a water flow in the passageway 4 generated by the float 2, and a flow is generated toward the float 2 by the water flow and is allowed to collide against the float 2 to generate a flow directed toward the bottom of the water.

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