Mermentau River at Mermentau

1. 16.00 ftBetween 16 and 17 ft, flood waters reach the gauge over the mermentau river.
2. 15.10 ftBetween 15.1 and 16.0 ft, flood waters reach the base of the southern pacific railroad bridge east of mermentau across an unnamed tributary.
3. 14.30 ftThe river is at its flood of record. Widespread major to catastrophic flooding will occur.
4. 13.40 ftThe river is near its 100 year flood level. Most of the community of mermentau is inundated with flood waters.
5. 13.30 ftWater reaches the roadway of the of U.S. 90 bridge east of Mermentau.
6. 10.00 ftWidespread flooding over a large area from Interstate 10 to Lake Arthur with numerous homes and roads flooded. The community of Morse will be inundated with water. Much of Estherwood will be inundated due to backwater flooding from Bayou Plaquemine. Areas around Gueydan will be inundated with water due to backwater flooding from Bayou Que de Tortue. Communities of Klondike and Lowery will experience flooding as well.
7. 9.50 ftWidespread major flooding will occur with residential flooding in and around mermentau to the lake arthur area. Numerous roads are inundated across a large area including u.S. 90, la 3166, la 1126, and la 92.
8. 9.00 ftSome residential flooding in and around mermentau will occur. U.S. 90 west of mermentau is closed. Operations at the shipyards are affected. Roads in the mermentau cove area are flooded and impassable. Some residences are subject to flooding along the river near lake arthur.
9. 8.50 ftSome residential flooding in mermentau will occur. Operations at Gulf Island shipyard can be affected. U.S. Highway 90 west of mermentau is flooded and subject to being closed.
10. 6.20 ftThe water reaches the roadway of the 13th Street bridge in the southern portion of mermentau.
11. 6.00 ftFlooding of the shipyard begins. Portions of castex landing, la 3166, become flooded and impassable.
12. 5.50 ftA few recreational camps and residences are subject to flooding.
13. 4.00 ftMinor lowland flooding near the river will occur.

Chance of flooding, September to November

The three-month chances are the River Forecast Centers’ long-range flood outlook, issued September 16, 2026.

Most recent crests

• October 1, 2022: 4.34 ft
• May 22, 2021: 7.48 ft
• October 15, 2020: 5.90 ft
• August 31, 2020: 5.46 ft
• May 14, 2019: 6.23 ft
• February 12, 2018: 3.41 ft
• May 6, 2017: 8.61 ft
• August 18, 2016: 10.68 ft
• June 16, 2015: 4.05 ft
• April 20, 2015: 4.77 ft

• UpstreamBayou Nezpique at Basile
• DownstreamMermentau River at Lacassine Wildlife Refuge
• Bayou Plaquemine Brule at Estherwood
• Bayou Queue De Tortue
• Mermentau River
• Bayou Des Cannes west of Iota
• Bayou Plaquemine Brule
• Bayou Mallet
• Bayou Lacassine at Lorrain Park

Forecasts by the Lower Mississippi River Forecast Center. Forecasts are issued routinely year-round. River forecasts for this location take into account past precipitation and the precipitation amounts expected approximately 48 hours into the future from the forecast issuance time.

Stage, flood stages, impacts and crest history from NOAA’s National Water Prediction Service. Streamflow and the daily record from the U.S. Geological Survey.