An open-channel transition is needed in most water conveyance channels to connect channel sections with different cross-sectional shapes, areas, bottom slopes, or their combinations. However, these transitions inherently create adverse pressure gradients, flow separation, turbulent eddies, and energy losses, presenting a long-standing hydraulic issue. This study investigated a warped transition (WT), a transition type favored for its smooth linking geometry, which connected a small rectangular upstream channel section to a large downstream trapezoidal section, and evaluated the effectiveness of installing a honeycomb in the WT in reducing turbulence and improving flow characteristics and hydraulic efficiency. The three-dimensional velocity field of turbulent flow was measured using an acoustic Doppler velocimeter. The results showed that the honeycomb effectively improved mean flow properties by enhancing the uniformity of primary flow and reducing the strength of secondary currents and reversed flow. The cell size of the honeycomb limited the formation of larger energy-bearing turbulent eddies. Compared to a conventional WT without a honeycomb, the modified transition exhibited less severe flow separation and lower turbulence intensities. Implementing a honeycomb is a practical and inexpensive intervention for both existing and new transitions. The findings of this study provide valuable insights for improving the design of water conveyance channels.