<p>This work investigates how a vertical cylindrical obstacle affects the dynamics and mixing of lock-release gravity currents. Gravity currents are produced in the laboratory and density fields are measured using an image analysis. Two Reynolds numbers, three submergence ratios and three flow blockage ratios have been tested. Results show that upstream of the cylinder, gravity currents propagation remains unaffected. Downstream of the obstacle, the front velocity decreases compared to the undisturbed case, with a deceleration becoming larger as the obstacle diameter increases. The deceleration does not trigger the transition from the slumping to the self-similar phase. Greater obstacle height causes an increased current thickness upstream of the cylinder, while larger diameters amplify both the thickness and the reflection of the dense current. The entrainment parameter remains unchanged across all tested configurations. Energy budget analysis reveals an enhancement of mixing in the presence of obstacles.</p> Graphical abstract <p></p>