It depends on the configuration seen. There are different lights visible depending on the relative headings of the vessels and relative sizes etc.
You are approaching the starboard side of another vessel
The other vessel is coming directly toward the observer, so both the port and starboard running lights are visible.
You are approaching a powerboat head-on
The other vessel is coming directly toward the observer, so both the port and starboard running lights are visible.
You are approaching a powerboat head-on
You are approaching a powerboat head-on
You are approaching a sailing vessel - head-on
Turn on navigation lights.
You are approaching the port side of another vessel
When operating in conditions of reduced visibility, such as fog or heavy rain, reduce your speed, use your headlights, and increase following distance. Stay alert, avoid sudden maneuvers, and use windshield wipers and defrosters to maintain visibility. Consider pulling over in a safe location if visibility becomes too poor to continue driving safely.
Turn on navigation lights.
Turn on navigation lights.