Groynes are widely recognized for their role in protecting river and coastal banks from erosion. Due to a reduction in velocity magnitude, the area downstream of the groynes becomes susceptible to sediment deposition, creating a favorable habitat for aquatic organisms and vegetation. In this study, a three-dimensional turbulent open-channel flow (Fr = 0.19) with a single groyne was numerically simulated using the ANSYS FLUENT code. The standard k-ε turbulence model was employed for turbulence closure, while the VOF method was used for free surface treatment. Furthermore, the case of a vegetated patch located at the lee side of the single groyne was also examined. Vegetation was modeled using vertical, rigid cylinders located near the downstream face of the emerged, impermeable groyne, within its recirculation zone. The emergent vegetated stems were arranged in a uniform, parallel array of eighteen (3 × 6). The computed velocities were found to be in good agreement with the experimental data of Rajaratnam & Nwachukwu (1983) as well as the numerical results of Koutrouveli et al. (2019). In the case of a single groyne without vegetation, the numerical results showed that a recirculation zone is created with a reattachment length that varies between 15b and 12b from the bed to the free surface, where b corresponds to the groyne length. Furthermore, a comparison of reattachment lengths as well as the flow structure between the vegetated case and the non-vegetated case was also conducted.