We report that aqueous solutions of high molecular weight chitosan display a regime of shear thinning at low shear rates that is consistent with the existence of an apparent yield stress. The concentration-dependent scaling of the apparent yield stress, sigma(0)(c)similar to c(2.8 +/- 0.2) in the concentration range c = 7.50-65.0 mg/mL, is consistent with a solution microstructure of fractal clusters. Dynamic light scattering measurements at high concentration indicate extremely slow microdynamics, consistent with the presence of a structured network or glassy fluid. At shear rates above yielding, a constant viscosity plateau was observed with concentration-dependent scaling below the gel point consistent with existing models of entangled and associating polymers. The addition of urea, a hydrogen bond and hydrophobic interaction disrupter, did not change the reported concentration-dependent scaling of the apparent yield stress or the plateau viscosity but did weaken the apparent yield stress magnitude by similar to 30% on average.