The effect of electrostatic interactions on the rheology of aqueous colloidal dispersions is a topic of long-standing interest. "Electroviscous effects" were first quantified experimentally in the semidilute regime by Stone-Masui and Watillon in 1968, substantiating an earlier dilute theory and subsequent predictions for pair interactions. Experiments demonstrating the development of yield stresses at higher concentrations, stimulating exploration of the fluid-to-solid transition and later characterization of plastic flow and melting transitions in the solid phase. More recently, an extensive parametric study of theology in the fluid phase, demonstrating the effects of particle size, ionic strength, and volume fraction. This paper reports a correlation for the low shear viscosity of. the fluid phase suggested by the semidilute theories, an effort that is complicated by incomplete knowledge of the surface charge and ionic strength at finite volume fractions.