Biologists investigating a fish kill in the Mississippi River Gulf Outlet determined the fish died because of low oxygen levels, the Louisiana Department of Wildlife and Fisheries reported.

LDWF received several reports on Sunday (Aug. 22) concerning a large fish kill around the MRGO.

LDWF biologists have confirmed that high nutrient content from the Mississippi River in combination with seasonal occurrences has been the cause of hypoxic conditions for years. Although essential in fertilizing the estuaries, in some cases the nutrient load is too great and hypoxic conditions arise.

Hypoxic events typically occur in late summer to fall, and are also associated with processes that bring deep low-oxygen water to the surface. 

Fish need an oxygen level of at least 3 parts per million to survive. Measurements taken by LDWF staff at various samples sites showed less than 1 part per million of oxygen at the bottom of the water. A "borderline" oxygen level of perhaps 3 parts per million was found at the top.

The only large concentration of dead fish was noted in a bayou immediately adjacent to the MRGO. An estimated 500 fish were found in the area. Based on the condition of the fish, they appeared to be roughly five days old.

Species observed included large red drum, sheepshead, hardhead catfish, spotted sea trout, croakers and stingray.

Seasonal fish kills are normally found in much of southern Louisiana associated with low oxygen events. LDWF biologists expect these to be common in areas such as marinas, dead-end canals and other areas with poor circulation.

To report a fish kill or abnormality, contact the nearest LDWF office during business hours or the Operation Game Thief operator (1-800-442-2511) after hours.

Coastal area offices are:

• Slidell
61384 Fish Hatchery Road
Lacombe, LA 70461

• New Orleans
2021 Lakeshore Drive, Suite 407
New Orleans, LA 70122

• Bourg
Post Office Box 189
Bourg, LA 70343

• New Iberia
2415 Darnall Road
New Iberia, LA 70560

• Lake Charles
1213 North Lakeshore Drive
Lake Charles, LA 70601