Distributions of shear stresses throughout the entire cross-section within the fully developed boundary layer region in both the smooth and rough surfaces of a rectangular open channel flow were experimentally determined. Velocity measurements were taken for two different surfaces and 48 flow conditions with Fronde numbers in the range: 0.12 <= Fr <= 1.23 and with aspect ratios within: 4.2 <= b/h <= 21.6. For all the flow conditions created in the setup, the local shear stress was computed using the universal logarithmic distribution. The relationships between the mean cross sectional shear stresses and the aspect ratio, and Froude numbers were determined for both smooth and rough surfaces. For all the flow conditions formed in the setup, the shear stress distribution along the cross section was succinctly expressed by a second degree polynomial. The maximum shear stress on the bed was found to be about 6-20% greater than the mean bed shear stress for smooth surfaces and 2-16% grater for rough surfaces, respectively.