What should the operator of a vessel do when they see a buoy with a red light?

When an operator of a vessel sees a buoy with a red light, it is an indication that they are encountering a navigational aid that marks the right side of a channel when approaching from the sea. In the context of navigational rules, these aids are designed to help guide vessels safely through waterways. Therefore, the proper action is to keep the buoy on the starboard side, which means it should be on the right side of the vessel as it heads towards the shore or upstream.

This practice is essential for safe navigation, as buoys are a critical part of marine navigation, helping to designate safe passage and warn of hazards. Maintaining the buoy on the starboard side signifies that the operator is following the correct navigational protocol in accordance with maritime law. The other options would not align with safe navigational practices.