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Coast Survey to Improve "Magenta Line"

The magenta line is a directional guide on Intracoastal Waterway nautical charts.

nautical chart showing magenta line

As charts are updated, the magenta line will generally be positioned in the centerline of dredged channels and natural waterways, avoiding shoals or obstructions.

On January 14, the Office of Coast Survey announced that future editions of nautical charts of the Intracoastal Waterway will be updated to include an improved “magenta line” that has historically aided navigation down the East Coast and around the Gulf Coast. Additionally, Coast Survey will change the magenta line’s function, from the perceived "recommended route" established more than a hundred years ago, to an advisory directional guide that helps prevent boaters from going astray in the maze of channels that comprise the route.

Why was the magenta line removed?

Last year, Coast Survey investigated problems reported with the magenta line. After receiving reports of groundings by boaters who followed the line into shoals, Coast Survey started to remove the magenta line from Intracoastal Waterway nautical charts.

In October 2013, as part of the investigation on the magenta line, Coast Survey issued a Federal Register Notice asking for public comments. With a response rate of 99% in favor of the magenta line because it supports safe navigation on the Intracoastal Waterway, Coast Survey decided to include an improved magenta line on updated charts.

When will I see a revised magenta line on my chart?

As Intracoastal Waterway charts come through the routine process for updates, Coast Survey will evaluate and update the magenta line using charted information. When no depth soundings are on the chart, the line will generally be positioned in the centerline of dredged channels and natural waterways, avoiding shoals or obstructions. When the chart data is insufficient for determining the line's preferred route, Coast Survey will attempt to gather additional data from partner agencies and reliable crowdsourcing.

Resolving chart discrepancies will take more time, possibly up to five years or even longer. In cases where information is lacking and the line depiction can lead to risky navigation, Coast Survey will remove that portion of the line.

One important update you will see on your nautical charts are notes emphasizing that vessels transiting the Intracoastal Waterway should be aware of changing conditions and always honor aids to navigation.

Brief History of the Magenta Line

The U.S. Coast and Geodetic Survey, a NOAA predecessor agency, first installed the line on nautical charts in 1912, when the advent of motor boating produced a demand for charts of the inland waters and shallower waters along the East Coast. The magenta line on Intracoastal Waterway charts received major updates in the 1935, thanks to an influx of funding from the Great Depression's Public Works Administration projects. Charts rarely recorded updates of the magenta line in the ensuing 70 years.