The results of the research on the circulation and the mixing of lake water were organized, and the perspective of the research was considered. The flow of lake water is divided into a horizontal flow and a vertical flow. A horizontal flow is chiefly caused by the wind shear stress. As for the research of the flow caused by the wind shear stress, a field observation, a model flume experiment, and a numerical experiment have been conducted. They provided a remarkable advancement from the 1970s to the 1980s. Hereafter, using a new technology such as GPS will be hoped in the flow observation.
A vertical circulation is caused by the density difference of water due to the cooling on the lake surface and the wind shear stress. A vertical circulation causes the mixing of lake water. The mixing of lake water is investigated by observing the water quality distribution, especially there are a lot of researches that consider a vertical mixing making use of the profiles of the dissolved oxygen. In a tropical lake, there is a close relationship between the mixing of lake water and the heat balance on the lake surface, then the depth of vertical mixing is estimated by the amount of cooling on the lake surface. Therefore, it is considered that the clarification of the lake water mixing on a tropical lake contributes to the information about the global warming phenomenon. Moreover, some natural lakes are expected as a monitor of acid precipitation and the micro pollutant.