Temple Inland pleaded guilty to charges related to a fish kill near its plant in Bogalusa in August of 2011.
Sentencing is set for May 1.
A discharge from the company's plant into the Pearl River depleted Oxygen levels in the water.
For violating the Clean Water Act it could be fined up to $200,000 dollars.
The company could be hit with a $10,000 fine per taking for violating the Refuge Act.