[PROBLEMS] To provide a water quality improvement system capable of realizing an improvement in water quality at a low cost even in the case where a closed water area to be improved is wide. SOLUTION: A floating body Bo suspended on a target water surface that is an object of water quality improvement, and a gas-liquid mixing processing device C3 mounted on the floating body Bo, and the gas-liquid mixing processing device C3 sucks the target water. Then, the aspirated target water and the fluid for improving the water quality are mixed to form mixed treated water, and the mixed treated water is reduced to the target water. [Selection] Figure 1【課題】水質を改善すべき対象の閉鎖系水域が広範囲にわたる場合であっても、安価なコストで水質の改善を実現することができる水質改善システムを提供すること。【解決手段】水質改善対象である対象水面上に浮遊させた浮体Ｂｏと、浮体Ｂｏに搭載した気液混合処理装置Ｃ３と、を備え、気液混合処理装置Ｃ３は、対象水を吸引するとともに、吸引した対象水と水質を改善する流体とを混合処理して混合処理水となし、混合処理水を対象水中に還元させるようにした。【選択図】図１
