Riparian vegetation, which is commonly found in natural rivers and open channels, has a strong influence on flow structures. This paper describes a laboratory experiment on velocity distributions, secondary currents, and coherent structures in narrow open-channel flow under the influence of submerged riparian vegetation. The channel is divided into a near-bank vegetated zone (VZ) and a main channel (MC) between which horizontal shear-induced coherent structures take place. A Prandtl mixing length model is applied to estimate the lateral distributions of horizontal Reynolds stress. Based on the experimental data, patterns of secondary currents induced by riparian vegetation in a narrow open channel are reported for the first time, which are found to be the cause of an S-shaped vertical profile of longitudinal velocity at the VZ-MC interface. This S-shaped velocity profile further results in two vertical mixing layers where vertical shear-induced coherent structures develop leading to correlations between longitudinal and vertical velocity fluctuations. Secondary transversal velocity also influences the characteristics of horizontal coherent structures close to the VZ-MC interface, that different inclination directions (clockwise or anti-clockwise) of these coherent structures are observed at different depths corresponding to the local transversal velocity.