What flag signifies that divers are over the side during the day?

The correct answer is the rigid flag "Alpha," which is an internationally recognized symbol indicating that divers are in the water and boats should keep their distance. The Alpha flag is a blue and white flag, specifically designed for this purpose, alerting other vessels to the presence of diving activity nearby. When this flag is displayed, it signifies that there are divers below the surface, creating a heightened risk that other vessels should be aware of in order to avoid potential accidents or injuries.

Using the Alpha flag is critical for safety on the water; it helps ensure that divers can operate without the added concern of nearby boat traffic. The flag's unique design makes it easily identifiable, which is essential for effective communication among vessels operating in and around diving areas. It emphasizes the need for vigilance from other boaters to maintain a safe distance and protect the individuals who are diving.