What does a red flag with a diagonal stripe indicate?

A red flag with a diagonal stripe is a visual signal that indicates that water skiing activity is in progress. This flag serves as a warning to other boaters and individuals in the vicinity that water skiers are actively using the area, thus they should exercise caution. Displaying such a flag helps ensure the safety of both the skiers and nearby vessels by alerting them to the presence of water skiing activities, which can create hazards if not properly communicated.

In contrast, while other flags serve different purposes in signaling restrictions or activities—such as prohibiting swimming or indicating areas where fishing is not allowed—none of these other flags convey the specific message associated with water skiing.