The clogging of porous media by colloidal particles is a complex process which relies on many different physical phenomena. The formation and the structure of a clog results from the interplay between hydrodynamics (flow rate and pore geometry) and the DLVO forces (particle–particle and particle–wall). In order to get a better understanding of this process, we study the clogging of a microfluidic filter, at the single pore level, and determine the influence of each relevant parameter separately. We show that in order to form stable clogs, colloidal particles have to pile up over a length in the flow direction roughly equal to the width of the pore. We found that there are two clogging regimes, which depend on the applied pressure. In the first one, at low pressures, the length of the clog within the pore and the number of particles that pass through the pore prior to clogging are constant. In the second one, for higher pressures, both quantities increase with the pressure. We also show that a higher ionic strength accelerates the clog formation, keeping constant the length of the clog