MRGO – Mississippi River Gulf Outlet

MRGO – Mississippi River Gulf Outlet

The Mississippi River Gulf Outlet (MRGO) is a 76-mile long artificial channel that was constructed to provide a shorter navigation route between the Gulf of Mexico and the Port of New Orleans.  Authorized by Congress in 1956 and completed by the U.S. Army Corps of Engineers in 1968, the MRGO originally was 650 feet wide at the top and at least 36 feet deep. More earth was dredged to construct the MRGO than was moved to construct the Panama Canal!

Proposed as an economic development project, the MRGO was lightly used and expensive to maintain (dredging, etc.). In 2006, the MRGO cost taxpayers nearly $20,000 for each vessel traveling in the channel. The MRGO also came at a steep environmental price, which scientists and communities along the MRGO had anticipated before the Corps started construction. When the Corps dredged the channel, they converted 20,000 acres (31.2 square miles) of wetlands to open water, and allowed saltwater to flow inland from the Gulf, eventually damaging an additional 7,600 acres (11.8 square miles) of wetland and lagoon habitat. By 2005, erosion along the channel’s banks expanded the MRGO to a width of 3,000 feet in some areas, bringing it in close proximity to the hurricane protection levee. Saltwater moving up the channel also damaged or destroyed freshwater cypress forests of Orleans and St. Bernard Parishes, and created a dead zone in Lake Pontchartrain. All told, the construction and operation of the channel has impacted more than 618,000 acres (965.6 square miles) of habitat—an area almost three times the size of New York City’s five boroughs.

When communities like the Lower Ninth Ward, Arabi, and Chalmette were established, a natural storm buffer of cypress trees and other wetlands helped protect them from hurricanes. The MRGO put those communities at risk by damaging or destroying that protective buffer. Despite being at a higher elevation than much of New Orleans, St. Bernard Parish and the Lower Ninth Ward experienced the deepest, most violent flooding in the New Orleans metro area during Hurricane Katrina. According to a 2009 report by eight expert scientists, the extensive flooding in this area was directly attributable to the MRGO. Through detailed wave and hydrodynamic modeling, the scientists showed that waves in Lake Borgne were able to rebuild to 8 to 9 feet high as they crossed the MRGO channel, breaching the earthen levees along the channel while the surge was still rising. The flooding was also worsened by the levee-lined intersection of the MRGO and the Gulf Intracoastal Waterway, which funneled storm surge through the MRGO and into the Industrial Canal—flooding the heart of the city. During Hurricane Katrina, the fierce surge and waves caused levees and flood walls to collapse and unleashed a wall of water into densely populated communities east of the Industrial Canal.

Map showing the location of the MRGO, GIWW, the two closures at the rock dam and the surge barrier as well some of the large neighborhoods affected by the storm surge from Hurricane Katrina.

Dredging of the MRGO in 1958 (left, Army Corps of Engineers, via The Associated Press), MRGO groundbreaking in 1957, notice the dead logged cypress in the background and the dynamite blast in the swamp (middle, Army Corps of Engineers, via The Associated Press) and a cartoon depicting the MRGO as a bowling alley that allowed storm surge from Hurricane Katrina to knock New Orleans down like bowling pins, essentially painting it as a hurricane super highway (right,

An aerial view of the Lower 9th Ward before Hurricane Katrina (left) and immediately after (right). After the hurricane, most houses in the Lower 9th Ward were flooded causing widespread destruction.

Closure of the MRGO

(email for access to bold print documents - no hyperlink) Following Hurricane Katrina, a group of prominent Louisiana coastal scientists released a report detailing the impacts of the MRGO and recommending its closure. In 2006, the MRGO Must Go Coalition, a group of 17 local and national non-governmental and community organizations, was formed to advocate with St. Bernard and Orleans Parishes for the closure of the MRGO and restoration of the ecosystem. Advocacy efforts resulted in the deauthorization of the MRGO and requiring that the channel be closed to navigation. This was accomplished by construction of a 950-foot rock dam across the channel, along the Bayou La Loutre Ridge, a natural ridge in St. Bernard Parish that was breached for the construction of the channel. Additionally, the Inner Harbor Navigation Canal-Lake Borgne Surge Barrier was constructed at the top of the MRGO to provide a second closure and additional protection. As part of the deauthorization, congress mandated that the Corps develop a MRGO Ecosystem Restoration Plan  which was completed in 2012.  The plan was influenced by record-setting public input and advocacy efforts. The plan outlines restoration projects and other activities to repair and restore the MRGO ecosystem.

The rock dam closed the MRGO at the bottom, in line with the Bayou la Loutre Ridge (top) and the surge barrier provided a second closure at the top of the MRGO near New Orleans (bottom). The MRGO can be seen going off into the distance on the picture on the bottom left.

MRGO Ecosystem Restoration

MRGO ecosystem restoration, critical to protection of the Greater New Orleans Area, still waits for funding and implementation of keystone projects. Despite strong public support for implementation of the restoration plan, no funding has been appropriated to the Corps for further study or construction regarding ecosystem restoration in the MRGO impacted areas. Continuing conflicts between the Corps and the State of Louisiana over the State’s cost-share for restoration make it unlikely that the plan will be implemented in the foreseeable future. Comprehensive restoration of the wetlands impacted by the MRGO is critical to achieving maximum resilience for New Orleans and surrounding communities and must be made a priority.

While the Corps plan for restoration has not been funded, some of the projects or portions of the project proposed in that plan are in the State of Louisiana’s Comprehensive Mater Plan for a Sustainable Coast as well as proposed by the state for RESTORE funding (penalties from the BP oil spill). Comprehensive restoration of the MRGO ecosystem is essential to repairing the damage done by the dredging and negligent operation and maintenance of the MRGO channel as well as re-establishing the natural lines of defense that protect the surrounding communities and levee system.

The U.S. Army Corps of Engineers in the approved MRGO ecosystem restoration plan. A combination of marsh and swamp nourishment and restoration, shoreline protection, ridge restoration, MRGO canal restoration and oyster reef restoration are proposed.


(please email for access to resources)


2009 MRGO Bathymetric (Depth) Map


Unified Deauthorization Plan Report 12-5-06
MRGO Rock Dam Survey 5-06-09
MRGO Must Go Coalition Report April 2010
MRGO Ecosystem Restoration Plan 2012 (USACE)


2009 MRGO Ruling
MRGO Ruling of Appeal