Phase-averaged 2D planar PIV data for an optimal and sub-optimal tip-speed ratio (? = 1.1 and 1.9, respectively) is captured over the upstream and downstream sweep of two-bladed, straight bladed cross-flow turbine. The azimuthally varying near-blade hydrodynamics are examined in concert with phase-averaged performance data. Both the near-blade and near-wake hydrodynamics are shown to be highly dependent on tip speed ratio and azimuthal position and the implications on power production are discussed. The flow field surrounding downstream blades appears to be critical to overall turbine performance, with strong and persistent stall and vortex interactions appearing to lead to downstream blade forces that exceed increases in lift on the upstream blade due to a strong leading-edge vortex at ? = 1.1. Upstream blade vortex shedding is significantly delayed for ? = 1.9. This, combined with a weakly stalled downstream blade, yields a significant increase in turbine performance. Differences between flow patterns observed in this and previous studies suggest an influence of Reynolds number.