Non-chlorinated actual brackish lake water was used as feed to examine the fouling behaviour, includes biofouling and cleaning effects of forward osmosis (FO). Fouling experiments were conducted at different filtration time durations on thin film composite (TFC) membrane in FO mode (active layer facing the feed). Fouling was formed on membrane surface and followed an exponential trend during the experimental period. Microbiological assays and fluorescence excitation-emission spectrophotometer were used to examine the details of the foulants and provide information on the physiological state of the membrane foulants in the FO system. The results indicated that the fouling observed was the combination of bacterial biomass (biofouling) and protein-like organic constituents derived from microbial activity (organic fouling). At the end of the 24 h fouling experiments, the water flux declined by approximately 65% of the initial value. However, the flux was completely recovered to its initial level following hydraulic cleaning by deionized (DI) water; the fouling on the FO membrane is found to be reversible. (C) 2014 Elsevier B.V. All rights reserved.