In US waters, green can buoys mark a channel’s left port side and red nun buoys mark the right starboard side when you are heading inland from the sea.
Approaching an unfamiliar harbor at dusk, the two nearest buoys can look like a matched pair — until you notice one is a flat-topped can and the other tapers to a point. That shape difference is the whole system. Get it wrong and you are on the wrong side of the channel, which is exactly where the shallow water lives.
US inland and coastal waters use IALA Region B: green means port, red means starboard, the reverse of most of the rest of the world. The federal rules sit in Title 33 of the Code of Federal Regulations, and the core definition lives in 33 CFR § 62.25, the lateral marks rule.
Which Buoy Marks The Left Side Of A Channel?
Green marks the port side — the left side of the boat as you face forward along the conventional direction of travel. The mark is normally a cylindrical can buoy or a pillar buoy, and a fixed beacon carrying that role shows a green square daymark.
Port-hand marks are numbered with odd digits, climbing as you head upstream or in from seaward. So a green can stamped “7” sits farther in than the one stamped “5.”
Red handles the other side: a nun buoy, the conical one that comes to a point on top, marks starboard. Fixed red beacons wear a triangular daymark, and the numbers are even.
The shorthand most boaters learn first is “red, right, returning.” Keep red on your right when returning toward a harbor, heading upstream, or moving toward the head of navigation. Leave that harbor outbound and the arrangement flips — red is now on your left.
How Do You Read Channel Buoys In Tricky Water?
One table covers the marks you will actually see, because most confusion comes from treating every buoy as a simple left-or-right call.
| Mark Type | What It Looks Like | What It Means |
|---|---|---|
| Port-hand mark | Green can or pillar buoy; odd number | Left edge of the channel when inbound |
| Starboard-hand mark | Red nun or pillar buoy; even number | Right edge of the channel when inbound |
| Preferred-channel mark | Red and green horizontal bands | Junction or obstruction; either side may work |
| Safe-water mark | Red and white vertical stripes | Mid-channel or fairway water, not an edge |
| Special-purpose mark | Yellow | Anchorage, cable area, pipeline, or zone |
The preferred-channel mark trips people up. At a fork, the top band’s color tells you which branch is preferred: a red top band makes the mark act as a starboard-hand aid, a green top band makes it a port-hand aid. That reading only holds for one direction of travel — turn around and the same buoy means something different, so check the chart rather than trust a color rule.
Safe-water marks are a separate category: vertical red and white stripes say “middle of the fairway,” not “edge.” Yellow marks are not lateral aids at all.
Buoys are also not the channel boundary, which surprises most beginners. Federal rules say sidemarks are not always placed directly on a channel edge, so the chart and local notices carry the real route. If you are outfitting a boat and want gear that holds up to a season of running marks, the tested buoy roundup on our sister page covers the options we have actually used.
What Errors Sink Beginners Fastest?
The most common mistake is running “red, right, returning” while heading outbound, which puts you on the wrong side of a marked channel without warning.
- Assuming every red mark is a channel edge — red and green together means a junction, not a boundary.
- Navigating by color alone at night. Color, shape, number, and light characteristic work together, and the Light List confirms the lighting pattern.
- Treating a shifted, damaged, or unlit buoy as proof the channel has moved. Report the discrepancy and use current charts.
- Applying US colors abroad. In IALA Region A, port is red and starboard is green — the exact opposite of home waters.
- Mistaking a buoy, which floats, for a beacon, which is fixed to the bottom or a structure. Both can mark a side.
None of this replaces the chart. A preferred-channel mark may guard a wreck or shoal rather than a clean split, and neither side is automatically safe to cross. Read the chart, check the direction of buoyage for that waterway, and then place the buoy where it belongs.
FAQs
Is The Green Buoy Always On My Left?
Only when traveling in the conventional direction, typically entering from seaward or heading upstream. Reverse course and green sits to starboard. The conventional direction is set per waterway and appears on the nautical chart, so confirm it before assuming which side is which.
Why Does A Red And Green Buoy Have Two Colors?
A mark with horizontal red and green bands flags a junction or obstruction. The top band sets the preferred branch: red on top favors starboard, green on top favors port. Check the chart to see which branch the preference applies to before you commit.
Do These Colors Work Outside The United States?
No. The US follows IALA Region B, where green is port and red is starboard. Most of the rest of the world uses Region A, which swaps those meanings. If you charter abroad, the lateral colors you memorized at home will point you the wrong way on the first day.
References & Sources
- US Electronic Code of Federal Regulations. “33 CFR § 62.25 — Lateral Marks” Defines port and starboard color, shape, and numbering conventions for US lateral marks.
- US Electronic Code of Federal Regulations. “33 CFR § 62.21 — General” Covers buoyage direction, placement of sidemarks, and general aids to navigation rules.