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Background This paper investigates the effectiveness of dense vegetation on removal of colloids, which are important nonpoint source pollutants. In small scale colloid transport experiments, the deposition rate of colloids in dense vegetation is often taken as constant. Results This assumption was tested by experiments and modeling aimed at quantifying changes in colloid retention during transport in dense vegetation, in particular how colloid retention changes with travel distance. Flume experiments using a 10-m long dense vegetated strip were conducted under various conditions with combinations of different flow velocities, initial colloid concentrations, solution pH and ionic strength. The advection-dispersion model coupled with first-order deposition kinetics simulated the experimental data satisfactorily. Conclusions It showed that the colloid deposition rate decreased with travel distance, with the decline following a power law, and reached steady state after about 10 m. Diffusion and interception processes in colloid filtration theory were sufficient to describe the observed deposition kinetics. The decreasing trend in colloid deposition could be attributed to decreased diffusion along the travel path.