Modelling the interaction of benthic (bottom dwelling) and pelagic (open water) grazers and their planktonic food requires an understanding of hydrodynamic transport mechanisms as well as grazer feeding responses to this transport. I will present empirical data from open-channel flow chamber studies that demonstrate that the clearance rates (volume of fluid cleared of particles per individual per unit time) of freshwater mussels varies uniomodally with algal flux. A similar response was found for the clearance rates of planktonic $Daphnia$ $magna$ (water flea) in response to vorticity (solid body rotation). Whereas the mechanisms underlying these feeding responses may differ, the similarity in pattern suggests a consistency, which should be amenable to modelling.