A shear stress sensor for measuring the shear force of a fluid flowing along a wall. A floating member, flush with the wall, senses a shear force of the flowing fluid. The floating member is mounted by support means to a base element that is placed in the wall, so that the floating member is flush with the wall and a shear force, sensed by the floating member, is translated via the support means to a Fiber Bragg Grating. The force acting on the Fiber Bragg Grating changes the shape and the refractive index of the Fiber Bragg Grating, thereby changing the resonant frequency of the Fiber Bragg Grating and causing a shift in the spectrum of wavelengths of light that is introduced to the Fiber Bragg Grating. This shift in the spectrum of wavelengths is representative of the shear force of the flowing fluid.