The correct answer is A) water comes over the foredeck of the lead barges. When a towboat is pushing barges at an excessively fast speed, the speed can cause water to come over the foredeck of the lead barges. This indicates the towboat is operating at an unsafe speed that exceeds the maneuverability and stability of the tow. Regulations require towboat operators to maintain a safe speed that allows them to properly control the tow and avoid dangerous conditions. The other options are incorrect because they do not directly indicate an unsafe speed. A roostertail exceeding the height of the main deck (B) may simply indicate a fast speed, but not necessarily an unsafe one. Vibration when backing down (C) and strain on the face wires (D) are more related to other factors like tow configuration or machinery issues, not necessarily speed.