A middle of May, 1992, joint investigation by the lake Biwa Institute of Japan and the Dali Prefecture Environmental Science Institute on the ecological condition of Erhai Lake showed that although it was the end of the dry season then, the physical and chemical aspects of the water quality of the lake were still good because there was a rich water period last year, so ever`if it was the end of dry season then, the lake water level was still relatively high. The study results provide scientific basis for the protection of the lake environment and rational management of Erhai Lake whose ecological condition had been somewhat adversely affected by too large scale culture of fish.