Bayou Manchac is an 18-mile-long (29 km) bayou in southeast Louisiana, USA. This bayou was once a very important waterway linking the Mississippi River (west end) to the Amite River (east end). East Baton Rouge Parish lies on its northern side, while its southern side is divided between Ascension Parish (to the east) and Iberville Parish (to the west). The large unincorporated community of Prairieville and the city of St. Gabriel both lie on its southern side. Dr John R. Swanton a linguist who worked with Native American languages suggested that the name Manchac is derived from Imashaka which is a Choctaw word meaning "the rear entrance". 
Pierre Le Moyne d'Iberville made his way up the Mississippi and discovered what is now the city of Baton Rouge and wished to find a quick way back to the Gulf of Mexico, where his ships were moored at Ship Island. The chief of the Bayogoula tribe, who had accompanied him to the future site of Baton Rouge, on March 26, 1699 showed him the bayou which the Bayogoula used to travel between the present-day Mississippi Gulf Coast and their village.  Though it once formed an international boundary, attempts to navigate the bayou as a shortcut between the Mississippi and Amite rivers, or to make it navigable, were generally unsuccessful.
In 1764 the British established a trading post on the Iberville River and called it Fort Bute at Manchac.  The British traded with boats travelling down the Mississippi and encouraged trading at Manchac rather than with the Spanish further down at New Orleans. The fort at Bayou Manchac was a strategic position for the British and positioned to compete with Spain for the 100,000 pounds sterling per-year fur trade. 
San Gabriel de Manchac
Soon after the British built Fort Bute the Spanish responded by building a trade post on the opposite side of the river.  On September 28,1766, an English ship arrived in New Orleans from Maryland and it was carrying 224 exiled Acadians. The Spanish Governor Antonio de Ulloa at the Isle of Orleans gave them supplies and they settled around San Gabriel de Manchac. 
Industrial use and today
Bayou Manchac became one of the most important waterways of southeastern Louisiana. It served the vital role of linking Baton Rouge to Lake Pontchartrain via the Amite River and Lake Maurepas. Through time, as ships became larger and faster, Bayou Manchac was too small to support modern traffic. In the 20th century, when the levees were built, Bayou Manchac was cut off from the river, and later the upper sections dried out or were cut off by roads. Now the bayou is only useful for drainage and recreation, but the area is still regarded by those who live in the vicinity as one of Louisiana's most beautiful examples of nature.
- U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map Archived 2012-04-05 at WebCite, accessed June 20, 2011
- William A. Read (12 October 2008). Louisiana Place Names of Indian Origin: A Collection of Words. University of Alabama Press. p. 40. ISBN 978-0-8173-5505-0.
- James Dunwoody Brownson De Bow (1854). Encyclopaedia of the Trade and Commerce of the United States: More Particularly of the Southern and Western States: Giving a View of the Commerce, Agriculture, Manufactures, Internal Improvements, Slave and Free Labour, Slavery Institutions, Products, Etc., of the South ... Trübner & Company. pp. 1–.
- Mary Ann Sternberg (April 2007). Winding Through Time: The Forgotten History and Present-Day Peril of Bayou Manchac. LSU Press. pp. 47–. ISBN 978-0-8071-3577-8.
- James Dunwoody Brownson De Bow (1852). The Industrial Resources, Etc., of the Southern and Western States: Embracing a View of Their Commerce, Agriculture, Manufactures, Internal Improvements, Slave and Free Labor, Slavery Institutions, Products, Etc., of the South : Together with Historical and Statistical Sketches of the Different States and Cities of the Union : Statistics of the United States Commerce and Manufactures, from the Earliest Periods, Compared with Other Leading Powers : the Results of the Different Census Returns Since 1790, and Returns of the Census of 1850, on Population, Agriculture and General Industry, Etc. : with an Appendix. Office of De Bow's review. pp. 29–.
- Barry Jean Ancelet; Jay Edwards; Glen Pitre (20 January 2012). Cajun Country. Univ. Press of Mississippi. pp. 15–. ISBN 978-1-60473-617-5.