Water flows horizontally through a narrow channel over a heated superhydrophobic surface with a rib-patterned microstructure. A camera views the surface (top down) through a glass slide which forms the top of the channel. Air dissolved in the water effervesces as the water temperature rises and nucleates on the air-filled microscale cavities. Bubbles grow from the nucleation sites, merge together, and are eventually swept away. The geometry of the microstructure influences the nucleation and growth of the air bubbles. Ribs perpendicular to the flow form bubbles which span the channel, ribs parallel to the flow form few bubbles, and ribs parallel to the flow with sparsely-spaced perpendicular ribs retain bubbles which span only a portion of the channel width.