Light is never being distributed homogeneously and it forms a gradient over biomass. The unidirectional nature of light gives rise to a vertical gradient of light intensity as a function of Depth. The maximum Depth of the light zone suitable for phytoplankton photosynthesis is designated as the euphotic Depth. This study was designed to test the hypothesis of mixing Depth of phytoplankton and its compensation Depth. In a water column undergoing turbulent mixing, where phytoplankton cells are around by the fluid motion, the irradiance encountered by cells will be a function of the ratio between the euphotic Depth (zy) and the Depth of mixing (zm). During the course of study the zy/zm ratio value were observed in the range of 0.4427 to 3.242. However, identification of Compensation point values for zy/zm indicates that light conditions are suitable for net phytoplankton production, because the mean value (0.3413) was good for the phytoplanktonic growth, which was greater than the minimum 0.20 limit.