ICW: The Magenta Line

By Tom Hale

January 24, 2020

The magenta line was first added to charts in 1913. It was created to aid commercial navigation up and down the East Coast and around the Gulf Coast. To aid pilots running through the convoluted mix of waterways, a magenta colored line was drawn on the charts to indicate which rivers, creeks, sounds and canals were interconnected to provide an inshore route between the Chesapeake, FL and the Gulf Coast. The magenta line was merely like Hansel and Gretel’s breadcrumbs. It is drawn only as a means to find the path. The captains in those days monitored their course with, skill, experience, and hand bearing compass to know where they were on the ICW. For most of its life the magenta line was never edited or changed. With the development of GPS and chartplotters over the past 30 years some cruisers have assumed that the magenta a line is indeed a chartplotter route. It absolutely is NOT. It is meant as a trail of breadcrumbs to locate the path but not prescribe a route.

In 2014 the Office of Coast Survey tried to clarify the magenta line’s function, from the “recommended route” established more than a hundred years previously in an environment of vastly different navigation aids and tools, to an advisory directional guide that helps prevent boaters from going astray in the maze of channels that comprise the ICW. Chartplotters were not in wide use 100 years ago!

The change was the result of reported discrepancies with the magenta line. “We cannot deliberately include chart features that we know may pose a danger to navigation,” explained Rear Admiral Gerd Glang, director of NOAA’s Office of Coast Survey in 2014. “The problems of the magenta line’s misplacement, which had been developing over the past seven decades, were aggravated when some boaters assumed that the line indicated a precise route through safe water – although it actually went over land, shoals, or obstructions.”

In studying the ICW and making now 12 trips on it using NOAA charts, Navionics charts I can tell you that there isn’t just one “Magenta Line”. The so-called magenta line is not always the same on all charting systems. Some charts show the line in places from which it was eliminated on other charts. Some charts place it differently. The strip charts along the ICW shows the magenta line. The large-scale charts do not. The position of the line has changed over the years. I read comments on social media referencing the “magenta line”. Such comments lead to confusion, if not referencing the date of the chart and charting system being used. For instance, the magenta line at the west end of Snows Cut on a 2018 NOAA chart 11507 is not the same as a 2019 chart #3.

The magenta line is only drawn on the Intracoastal Waterway. There is no magenta line In the Chesapeake Bay, Delaware Bay, Hudson River, Long Island Sound or the Gulf of Maine. Those bodies of water certainly have hazards and shoals, but they are not a maze of rivers creeks and canals where it is easy to miss your turn. On the other hand, the New Jersey ICW is, like the Atlantic ICW, a maze of rivers creeks and channels where on it would be easy to miss your turn. There is a magenta line in the NJICW.

Whether you are running between Port Jefferson NY to Newport RI where there is no magenta line or Port Royal SC to Brunswick GA where there is a magenta line (with a few gaps), you are responsible for your own navigation. Be certain you have the latest charts. The best way to be sure is to use electronic charts which are easily updated with the touch of a button. The Notice to Mariners will not list any changes to the magenta line, making it hard to track any updates to the magenta line on your paper charts. Before you set out on any cruise, plan your own routes. These days it is common to share routes with other cruisers. Here too, it is important to know the date of the route. While a route plotted in the Chesapeake Bay in 2010 might still be adequate today. In Lockwoods Folly, the route I plotted in early April of 2019 would have run me hard aground by August.

Navigating the ICW is neither difficult nor dangerous. The secret lies in having access to multiple sources of information and plot your own course. For the most stress-free voyage along the ICW, use most up to date NOAA charts, and US Army Corps of Engineers Surveys available with Aqua Map Master and in particular have up to date Navionics Sonar Charts.

#1 Leaving the Pasquotank River and headed to the Alligator River near Wade Point NC the magenta line is almost 4 miles off the easily navigable waters.

#2 There is no magenta line in the frequently shifting route through Lockwoods Folly Inlet Crossing.

#3 The new “improved” magenta line at the west end of Snow’s Cut will not show on charts older than mid-2019.

#4a and #4b Little Mud River, the magenta line (highlighted as a red dashed line here) is in the center of the previously dredged channel. It crosses shoals of 4-5 feet, the yellow line is our track in water of 7-10 feet depth.

Even now with the new and updated magenta line, there is no official source (NOAA, USCG, USACE) which suggests that the magenta line should be used as a chartplotter route. Yes, you can run along the magenta line 95% of the time. Most of the way it is running though bodies of water where it does not matter if you are 100 feet or 200 feet on either side of the line on the charts. Heck, there are places you can be a mile or more to one side or the other and still be in deep water. (Picture #1) But there is no one sitting in an office monitoring the ICW hour by hour or day by day making changes to the magenta line.

Channels shift and change. The US Coast Guard promptly moves ATONs as conditions require. Often, as you transit these changing dynamic areas, you will see ATONs which are not on your chart The Office of Coast Survey does not even draw the magenta line through those especially dynamic areas where the channel frequently shifts such as Lockwoods Folly (Picture #2) and Mason Inlet crossings because they cannot keep up with the changes on a daily basis. When there is no recent data, no depth soundings are on the chart, the line will generally be positioned in the centerline of previously dredged channels which may not be where the deep water is found today. Little Mud River GA (Picture #3) , is a good example. There are other places where the magenta line has been recently updated such as at the New River Inlet crossing and at the west end of Snows Cut (picture #4).

When running along the ICW, if you do not update your charts and are not using the most recent updated NOAA chart, the chart you are relying on may not have latest buoy placement nor the latest guidance of the magenta line changes. You may be on magenta line, but not the most up to date magenta line. The magenta line is not drawn as a chart plotter route and should not be followed as if it were necessarily in the deepest water. While navigating the ICW keep your eyes on the buoys.