The Altamaha Riverkeeper filed the lawsuit last month against Rayonier Inc.'s mill in Jesup.
The lawsuit alleges that the factory discharges 50 million to 60 million gallons of waste into the river daily. The facility manufactures high-purity cellulose.
The lawsuit says the plant's runoff makes the river dark, and residents complain they can see and smell the discharged chemicals miles downstream.
The environmental group has asked a federal judge to order that the factory change its practices to comply with pollution rules.
Rayonier officials call the lawsuit "baseless" and say the firm has invested more than $70 million to limit colored discharges from the mill.
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