What does "Red, right, returning" refer to in navigation?

The phrase "Red, right, returning" is a mnemonic used in navigation to help boaters remember how to safely navigate through channels and into ports. Specifically, it refers to the practice of keeping red navigational markers (buoys) to the right side of the vessel when returning from sea towards the shore.

When a vessel is heading towards a harbor, channel, or dock, the red markers indicate the edges of the navigable waterway; thus, the boater should always have these markers to starboard (the right side of the boat) to ensure they are within safe limits and not running aground or hitting submerged hazards. This phrase reinforces safe navigation practices in areas where buoy systems are deployed, enabling mariners to navigate correctly and stay within the intended fairway.

The other options do not accurately describe the application of this mnemonic. For instance, while navigating upstream on a river might involve specific buoyage systems, it is not the general rule that "Red, right, returning" describes. The phrase specifically pertains to the context of a vessel returning to shore from the open sea.