Nanofiltration of surface waters has been successfully implemented at large scale facilities to improve water quality. In this work we examine the effect of several advanced pretreatment operations following conventional treatment by coagulation through filtration on membrane performance. Effluent samples of processes at a full-scale plant were obtained for subsequent treatment by membrane filtration in both dead-end batch filtration experiments and in cross-flow filtration. Dead-end experiments were designed to extract information on spontaneous flux as a function of recovery (up to 85%) while cross flow experiments were operated at a constant recovery of 75%. At the conclusion of each experiment, membranes were imaged by scanning electron microscope (SEM) and, in some cases, energy dispersive spectrometry (EDS) to obtain information on foulant structure and composition. Among the advanced pretreatment processes evaluated, granular activated carbon (GAC) pretreatment, combined with ozone, reduced fouling of both of the membranes tested to the greatest extent. Ultraviolet (UV) irradiation and pre-filtration through a 5um membrane did not measurably reduce fouling. Neither of these pretreatment processes appreciably reduced the total organic carbon (TOC) of the membrane feed. GAC pretreatment was further investigated in terms of the age of GAC used to perform the pretreatment. GAC age was not found to significantly affect fouling. This latter observation suggests that the primary benefit of GAC pretreatment may be related to biological activity on the GAC filters. Includes 5 references, tables, figures.