Charting errors can occur anywhere. There's a running joke among cruisers along Mexico's Pacific coast, about how the charts in certain areas - most recently surveyed in the 1860s by a US Naval vessel - are some 5 miles off. Everybody takes pictures of their chart plotters showing that their boat is on land, when - ha, ha - it's actually still floating just fine. The solution to those charting errors is to simply make sure you stay 5 miles offshore. It's pretty straightforward.
But there are stretches of the ICW with some serious charting errors, too. Problem is, unlike the Pacific Ocean, the ICW is only about 50 feet wide. So if you have a charting error, your margin of safety is very, very slim. Here are my pics:
This is The Fox, southbound along the ICW between Jacksonville and St. Augustine, FL. Observe we are center channel. The actual channel is steep-sided and much narrower than all that water leads you to believe; it gets very shallow as you approach either side. The water is so murky you can't see the shallows at all - your depth sounder tells you you're out of the channel when it suddenly goes from "enough water to keep floating" to "you have a problem." There are docks and McMansions to our left, and swamps to our right. Out here in center channel, our depth sounder is showing a comfy 7 feet of water under our keel at high tide (for a total of 13 feet of actual depth), and our knot meter has us scooting along at a nice 6.3 knots. Our chart plotter is that display over on the right side underneath our dodger.
The yellow areas are land. The white streak is the ICW. The line down the middle of the white streak is the theoretical center of the dredged channel. If I drove the boat following where my chart plotter says the center of the channel is? I'd be so far over to the left, I'd be driving The Fox into somebody's living room. Boy, would there be egg on MY face.
This is mildly amusing on a day with good visibility. But when you have to rely on your instruments at night? Or in fog? Or in heavy rain? Yeah: a real narrow margin of error.
I do not like the ICW.