Operations in weirs and ledges with hydraulics (or recirculations) are always associated with increased risk for the emergency services. The danger of being held beneath the water's surface due to strong downward currents is significant. In addition, the increased ratio of air to water reduces the buoyancy of boats and people. Water currents are not the only danger for emergency services. Unseen obstacles under the water's surface are also major hazards that are often greatly underestimated. Intensive, realistic training to develop experience, while applying safety precautions, is essential. In this film, to help avoid accidents, we want to look beneath the surface.