Navigating Green Square Daymarks: The Upstream Rule for River Travel

When piloting a vessel upstream (returning from sea), the lateral buoyage system follows a simple but critical rule: Green square daymarks mark the starboard (right) edge of the channel.

The "Red Right Returning" Mnemonic

The classic memory aid—"Red Right Returning"—means:

• Red = port (left) side when returning from seaward (i.e., going upstream)
• Green = starboard (right) side when returning from seaward

Therefore: Pass green square daymarks on your RIGHT (starboard) side when heading upstream.

Why This System Exists

The IALA Region B system (Americas, Japan, Philippines, Korea) standardizes this so mariners instantly know channel limits regardless of local geography. Daymarks (unlighted signs) complement lighted buoys for daytime navigation.

Practical Application

1. Identify direction: Are you going upstream (from ocean toward headwaters)?
2. Spot the mark: Green square (or triangle on lighted buoys)
3. Position vessel: Keep the mark on your starboard bow
4. Maintain channel: Stay between green (right) and red (left) markers

Common Mistakes to Avoid

• Confusing upstream vs. downstream direction
• Applying Region A rules (Europe, rest of world) where colors are reversed
• Ignoring daymarks in favor of GPS alone—visual confirmation is essential

Mastering this fundamental rule prevents groundings, collisions, and Coast Guard citations. When in doubt: Green square = keep right going in.