Field observations on internal waves in the North Basin of Lake Biwa were carried out during Biwako Transportation Experiment (BITEX'93). Rotary spectrum analyses of current show that beside the fundamental internal Kelvin waves, in the top epilimnion, there were waves rotating clockwise witb a period of 24h wbieh are thought to be wind-induced oscillations. In the tbermocline, pure Poincare waves of their first mode were found, which were the governing mode at the depth. The Poincare waves made the current at that depth rotate clockwise with a period of 16-18h. In (he hypolimnion bottom, seiehes with a period of 11 h were found which were not rotating and purely gravitational. All of these illustrate that there are different kinds of governing internal waves In different vertical zones. Internal wave research by current measurement, an important method, can distinguish the Poincare waves from internal seiches. The earth rotation effects are responsible for the current rotation, as well as wind rotation phenomena. Thus, the important physical factors on internal wave dynamics during stratification period in the lake seem to he wind stress stratification, Coriolis force and shore constrained.