Vertical flux of oxygen in lakes can play an important role in regulating the severity of hypoxia. Direct measurement of oxygen flux has remained hard due to lack of sufficient data. In this research, we focus on measuring vertical oxygen flux in a small hypoxic Canadian Shield lake using Fick’s Law = −K dDO⁄dz, where is the vertical turbulent diffusivity and () the vertical concentration of dissolved oxygen. To compute oxygen flux, a fast-response temperature and optical oxygen logger was attached to a temperature microstructure profiler and casts were obtained throughout the summer stratification period. The profiles were synchronized by aligning the temperature channels from the two instruments. To solve Fick’s Law, was obtained from the microstructure data using a buoyancy Reynolds number parameterization and ⁄ was obtained from the oxygen logger. The results show negligible oxygen flux through the thermocline (~ 3 × 10-4 gm-2d-1) during the summer stratification period, in comparison to the oxygen sinks in the hypolimnion (sediment oxygen demand and respiration).