Dianchi or Lake Dian is the largest shallow water lake on the Yunnan-Guizhou Plateau, which is not only crucial to maintain the ecological environments of Kunming, the famous city with four springs, but also contains almost 1.5×109 m3 highly polluted water. The management of the lake pollution and eutrophication will be a long-lasting hard work and the sudden diffusion of such highly polluted water can lead to catastrophic eco-environmental problems. Based on the historical documents, underwater topographic features, regional geological tectonics and the chronology of the sediments, it can be concluded that at one time the water leaked out in Dianchi, which is in consistent with the historical record of 1764 AD. This water leak event resulted in two funnels in the center of Dianchi. The sedimentary feature and the deformation properties indicated that the slope of one funnel collapsed, which means it was blocked, but the other one was under development or in dormancy. When the pressure induced from the water level changed or the earthquakes occurred, the underwater channel could be open or connected, a catastrophic water leakage might be induced. The highly polluted lake water would possibly flow to Lake Fuxian and pollute almost 9% national strategic fresh water resource, resulting in an eco-environmental event and endangering the national water security. Therefore, to monitor the water flowing situation, detect the position and direction of the channel, block the channel and prevent possible lake water leakage are the priority and urgent measurements at present.