Thermal Pollution

When human activities change the temperature of the water, we call this thermal pollution.  These temperature changes can negatively affect fish and aquatic life in Wisconsin’s surface waters and alter the water chemistry, which in turn impacts aquatic life.

Impacts of thermal pollution:

• Reduced reproductive success of fish and aquatic life
• Habitat degradation
• Fish kills (in extreme cases)

Common causes of thermal pollution:

• Coolant water: water used as a coolant for power plants and industrial manufacturers, then returned to the natural environment.
• Soil Erosion: Soil that washes into a water body makes it muddy and murky. This can lead to the water body absorbing more light and increasing in temperature.
• Deforestation: removing trees or plants that previously shaded a waterbody can expose it to sunlight causing the water to absorb more heat. 
• Runoff from paved surfaces: during the summer, paved surfaces (such as streets, driveways, and sidewalks) can get quite hot. As rainwater runs off of these surfaces it heats up before entering the storm sewer and draining to a nearby water body.

Learn more about thermally sensitive areas in Dane County and how the Dane County stormwater requirements help to protect thermally sensitive waters including trout streams. For additional information on thermal pollution, visit the Wisconsin Department of Natural Resources website.