Veteran AICW cruisers will tell you that the Waterway's passage across St. Andrews Sound, south of Jekyll Island, can one of the most daunting between St. Marys River and Norfolk, VA. To avoid a shoal in the sound, the AICW channel cuts almost out into the open sea before jogging back inland.
Recognizing the potential for rough water in anything even approaching bad weather, the US Army Corps of Engineers created an alternate route around St. Andrews Sound, back when the Waterway was constructed in the 1930's. Most authorities I've seen call this alternate passage, Umbrulla Cut, though the "cut" is but a small section of this channel, and, below, Captains Jim annd Lisa refer to this route as Floyd Creek. Actually, Floyd Creek is only the southernmost portion of the passage.
Whatever you call it, this can be a useful alternate route but ONLY at or within a hour of HIGH TIDE. I've sounded depths of as little as 4 feet in part of this alternate route at LOW water, and, these days, some soundings may even be shallower than that!
Please note that this message was copied from the AGLCA mailing list.

For those [cruisers] North bound on the ICW that are just getting into Georgia @ MM 694 you¹ll find Floyd Creek on your port side. If the winds have been kicking it up and it appears St Andrews Sound might be less then pleasant you have an alternative for a calm ride, as spelled out in Skipper Bob. We entered the Creek and headed NW, leaving the red buoy's to our port and green to starboard while in the Creek. If you go, go just before the high tide. We were half way through at an hour past high tide and never saw anything less then 8 feet and most was 12 to 18 feet. When you exit in to the Satilla River head NW and enter into @ G A17, follow creek and exit at G A5 in to the Little Satilla River and proceed W to Jekyll Creek and Jekyll Island where you rejoin the ICW. This route is 5 miles longer but worth the time if St Andrews Sound is sloppy or worse.
Jim & Lisa Favors – Kismet
 Fathom 40