"Now which side should the marker be on again?"
Friends, remember, you should have the red aids to navigation on the right side of your boat as you return to your port from the ocean. "Red Right Return."
If the river becomes part of the intracoastal waterway, as the Wilmington River does at the junction with the Skidaway River as you proceed inbound from Wassaw Sound, you no longer want the red marks on the right side of the boat. In the ICW, you want the red marks on the mainland side, or "Red Right going South."
That red beacon near the Savannah Yacht Club? Don't put it on your right as you head for Thunderbolt.
Your trip will be delayed:-)
(Look for the small yellow mark on an ICW lateral aid to navigation, be it a beacon or a buoy. Triangle or rectangle. It's small but it's there!)