Eventually, through a clerical error, Nementou became Mementou and this was then corrupted into Mermentau through confusion with the French word mer, which means "sea".

It was a crossing point for brave travelers on the Old Spanish Trail, but had such a bad reputation that until the Louisiana Purchase no one would go there to see how many people there were.

John Landreth was a surveyor who was sent from Washington, D.C., in 1818 to look for timber in Acadiana that could be harvested for the use of building Navy ships.

He kept a journal and had this to say: "...these places, particularly the Mermentau and Calcasieu are the harbours and Dens of the most abandoned wretches of the human race... smugglers and Pirates who go about the coast of the Gulph (sic) of vessels of a small draught of water and rob and plunder without distinction every vessel of every nation they meet and are able to conquer and put to death every soul they find on board without respect of persons age or sex and then their unlawful plunder they carry all through the country and sell at a very low rate and find plenty of purchasers."

[4] During the Civil War and the years immediately after it there were widespread reports of bushwhackers, robbers, and other fugitives hiding in the Mermentau woods and tales of hidden treasures in the area.

According to one of the stories, a man named Frank Quebedeaux once found an iron pot filled with coins.

Victorin Maignaud, another native of France, came to Mermentau in 1866 and opened a dry goods store.

On May 18, 1872, the Opelousas Courier reported: "For the last two weeks the streets of our town have been almost daily crowded with carts and wagons loaded with pieux, boards, and shingles coming from Pointe-aux-Loups and Mermento (sic).

Never has there been such a crowd at one time, and so successively we counted eleven ox-wagons in one expedition in one day this week.

In February of that year only 4 miles (6 km) of roadbed remained to be graded between Lafayette and Mermentau.

Passenger trains with sleepers attached were running a regular schedule from New Orleans to Houston by the end of September.

George W. Caldwell began carrying freight on the Mermentau about 1890, eventually owning a fleet of small boats and 24 barges.

Capt Caldwell also operated a commissary on the river front and issued metal tokens in denominations of 5,10, 25 and 50 cents and $1.

People from Crowley and elsewhere would take the train to Mermentau, then board the Olive for a weekend trip to Lake Arthur.

Mermentau is especially known for where Captain James Campbell, pirate Jean Laffite's most trusted lieutenant, stashed $9,000 in gold coins.

A total of 104,380 acres (422 km2) of marsh has converted to open water since 1932, a loss of 19 percent of the historical wetlands in the basin.