What kind of hazard can orange border marks typically warn about?

Orange border marks are specifically used in the marine navigation system to indicate areas where the public should exercise caution or are restricted from entering. These marks serve as warnings about operations under which navigation could become dangerous or restricted. A vessel operator may encounter various operational hazards, such as construction zones, military exercise areas, or areas where significant navigation hazards exist. This makes option B the correct answer, as it aligns with the essential purpose of orange border marks in informing mariners about potential restrictions in operations.

The other options do not accurately reflect the purpose of orange border marks. Underwater reefs, swimming areas, and caution for large vessels are indicated by different navigational aids or markers. For instance, underwater reefs are typically marked with safe water buoys, while swimming areas are often denoted by specified swimming area markers rather than orange borders. Therefore, the primary function of orange border marks as a warning for restricted operations distinguishes it clearly as the correct choice.