What does a green can buoy mark when you are returning from sea?

A green can is not a "can buoy" but a just a "can". Buoys are normally seen in deeper unprotected water. A can is characterized by the USCG as a Port Side lateral aid. When entering a channel from the sea heading into port the green aids will be on your left. They could be Buoys, Cans or Daymarks. The numbers on them will be odd. The same is true for the red aids. They could be Buoys, Nuns or Daymarks. Keep them on your right side when entering from sea. The reds will have even numbers. The numbers on the Navigation Aids increase as you travel towards the port, (not necessarily in order).

The ICW, (Intracoastal Waterway), does not follow the same numbering convention. Do not confuse it with a channel returning from the sea. When traveling the ICW the aids to navigation will have an extra yellow triangle or square indicating you are in the ICW. While in the ICW the red nuns / red daymarks will be on the mainland side of the channel. The green cans / green daymarks will be on the barrier island side of the channel.