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See national section for basic information and federal regulations.
Comparison: State vs. Federal
• Rules. Illinois follows the federal Clean Water Act in establishing limits for allowable thermal discharges into state waters. The limits established are based on the nature and location of the receiving water.
• Administration and enforcement. IEPA's Division of Water Pollution Control in the Bureau of Water is responsible for the administration and enforcement of the state's thermal discharge regulations.
As a general rule, Illinois dischargers may not create abnormal temperature variations in the water that would adversely affect aquatic life. The normal daily and seasonal temperature fluctuations must not raise the water temperature by more than 5°F (2.8°C).
In numerical terms, dischargers are prohibited from raising the temperature of the receiving water above the following limits for more than 1 percent of the hours in any 12-month period. At no time may these listed temperatures be raised by more than 3°F (1.7°C):