Micromechanics was used to show that the rupture strength of polymer-induced flocs varied with the hydrodynamic conditions at which the flocs were formed, A maximum flee strength at an intermediate shear rate was observed, The overall performance of the polymeric flocculants, as determined by two independent methods, showed that the conditions for optimal flocculation did not coincide with those for maximum flee strength. The amount of flocculation was explained in terms of the competing effects of the particle collision frequency and the destructive hydrodynamic forces, The contributing forces to the flee strength are, however, more likely to be densification of the flee by shear and the weakening of reattachment strengths, The evidence presented here may be useful for explaining flocculation data that depart from the constant yield stress theory. Thus, the notion of the flee strength varying with shear rate may offer an alternative to multilevel flee structure models in the description of flocculation kinetics.