Aids to Navigation assist the mariner by marking channels and advising of hazards. Furthermore, they provide an easy method of determining a boater's position. When returning from sea or to a harbor, red markers should be kept to the right and green markers to the left... hence the mnemonic, "Red Right Returning from the Sea". When traveling clockwise (Maine, to Florida, to the Gulf, to Washington State) on the ICW, the mnemonic changes to, "Red Right Returning from the North (or from clockwise, or from Maine, or however you best remember it)". It's important to note the two systems, because in many of the major inlets they overlap and cause the buoyage system for ICW travelers to reverse (Buoyage for the big ocean going traffic takes precedence). For clarity, ICW markers have yellow tags which use shape to denote its usage. So in these instances, a yellow square may be on a red triangle-shaped daymark.
Aids to navigation serve several purposes: Lateral Channel Markers, Safe Water Markers, Preferred Water Markers, Isolated Danger Markers, Range Markers, and Daymarks having no Significant Lateral Significance.
Lateral Channel Markers are either red or green and come in four major types: Light, Lighted Buoy, Can (green) or Nun (red) (both are buoys), and Daymark. The type used is at the discretion of the CG and is based on cost, type of hazard, visibility, other buoyage in the area, etc. The main thing is to follow the rules above and keep the Red markers on the Right when Returning. Here's what they look like:
Safe Water Markers are red and white and are not numbered; however, they may be lettered. They mark safe water. Here is one example.
Preferred Channel Markers are red and green and are not numbered; however, they may be lettered. This marker would typically sit at the middle of a fork in the river. The top color marks the color of the major channel, the bottom indicates the color for the secondary route. Here is one example. If you are headed south on the ICW and see this in front of an island, which way would you expect to be the safest way around the island?
Isolated Danger Markers are black and red and are not numbered; however, they may be lettered. They mark an isolated obstruction such as a shoal, a submerged object, etc. Here is one example.
Range Markers indicate mid channel when two markers are aligned. Typically, there is a center stripe on each. Color combinations may be green and white, white and black, white and red, red and black, green and black, or green and red. Here is one example. If the bottom marker appeared to right of the top marker, which way should you steer to get back to the center of the channel?