The Calcasieu Ship Channel is a waterway that connects the city of Lake Charles, Louisiana, with the Gulf of Mexico.

Its existence allows the Port of Lake Charles, which is more than 30 miles from the Gulf, to be the 10th largest seaport in the United States.

The primary use of the channel is the importation of materials for processing in Lake Charles' large refinery industry, including petroleum, liquefied natural gas, and the export of refined products, such as gasoline and chemicals.

Through the GIWW the Sabine and Calcasieu estuaries became co-mingled with saltwater intrusion which resulted in the combined Calcasieu-Sabine Basin.

By widening and straightening the Calcasieu River (removing the natural Sinuosity), as well as dredging, the Port of Lake Charles has been able to handle larger ships.