If you see a quick-flashing green light on a buoy ahead of you while heading downstream, where should you leave the buoy?

A quick-flashing green light on a buoy indicates that it is a lateral marker, specifically a green can buoy, which typically marks the starboard side of a channel when approaching from the upstream direction. Therefore, when you see this buoy while heading downstream, it is important to leave the buoy to starboard.

This is consistent with the conventional navigation rules, where green buoys are to be kept on your right side as you navigate towards the mouth of the river or harbor. Following this guidance ensures that you are proceeding safely and correctly through the waterway, maintaining proper channel navigation according to standard maritime practices.

If a vessel were to pass to the left of the buoy, it would be traveling in the incorrect direction with respect to the established navigational channel, which could lead to potential hazards such as grounding or collision with other vessels. Thus, leaving the buoy to starboard is the correct action for safe navigation in this situation.