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About Water Quality

Indiana’s water is part of the global hydrologic cycle, which occurs when water is distributed and moves between the earth’s atmosphere, land, and rivers, lakes and oceans, carrying with it all the dirt, pollutants, and disease-causing organisms that get into it. Every day, Hoosiers use water that comes from a river, lake, or underground and then is returned to the natural water system.

Water quality describes the chemical, biological, and physical characteristics of water. "Good" or "bad" water quality is not a simple determination since there are various types of beneficial water uses, including:

  • Habitat for aquatic life
  • Public water supply
  • Recreation
  • Agricultural
  • Industrial

Water quality is affected by various types of pollutants, including:

  • Turbidity
  • Pesticides
  • Fertilizers
  • Heavy metals
  • Sewage effluent
  • Industrial chemicals

IDEM has established water quality standards to protect the beneficial uses. The standards, based on supporting the various beneficial uses, establish the acceptable levels or ranges for various water quality parameters, including temperature, dissolved oxygen, and pH. These parameters are important measures of water quality. Each parameter affects one or more of the beneficial uses listed above. IDEM reviews and updates its water quality standards every three years.

IDEM and others monitor water quality parameters in streams and other waterbodies throughout Indiana. Waterbodies that are not within the standards are listed as "water quality impaired." The list of impaired streams is called the "303(d) List of Impaired Waters," after section 303(d) of the 1972 Clean Water Act.

For each stream on the 303(d) list, IDEM determines the total maximum daily load, or TMDL, allowable for each parameter. TMDL is a limit on pollution, developed when streams or other waterbodies do not meet water quality standards. TMDL plans consider both human-related and natural pollution sources. Streams can be delisted once IDEM’s TMDL plans are approved by the U.S. EPA, when monitoring shows that the stream is meeting water quality standards, or if evidence suggests that a 303(d) listing was in error.

Water quality varies naturally with location and time. For example, solar radiation influences stream temperatures throughout the day, and natural differences in climate and riparian vegetative cover cause differences in stream temperature. Some streams are just "naturally" warmer than others. Disturbances such as fires, windthrow (trees uprooted by wind), or even channelized debris flow can influence stream temperature, turbidity, and other water quality parameters. Geology, geomorphology, and climate change also influence water quality.

Pollution can make water unclean to the point where beneficial uses are harmed. Water pollution originates from either "point" or "nonpoint" sources:

  • Point source pollution is associated with a specific site on a stream and typically involves a known quantity and type of pollutant that can be controlled at the site. An example of point source pollution is effluent from a factory outlet (an end-of-pipe discharge) delivered directly to a stream.
  • Nonpoint source pollution results from multiple contaminant sources over a broader area than a point source. As rainfall or snowmelt flows over and into the earth’s surface, it picks up and carries away natural and human-made pollutants and deposits them into lakes, rivers, wetlands, and groundwater. Nonpoint source pollution can include:
    • Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas
    • Oil, grease, and toxic chemicals from urban run-off, energy production, and marinas and boaters
    • Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks and sand from eroding shorelines
    • Salt from irrigation practices and acid drainage from abandoned mines
    • Bacteria and nutrients from livestock, pet wastes, and faulty septic systems
    • Atmospheric deposition (when air pollutants settle on the earth’s surface)

Nonpoint source pollution is more difficult to manage and monitor than point source pollution. The volume or "load" from individual sources is difficult to measure. Water quality may not even be degraded at any of the source sites. Instead, the accumulated impacts of multiple sources of pollution can cause the water quality problem.

Pollutants can have harmful effects on drinking water supplies, recreation, fisheries, and wildlife. IDEM offers tools for communities and guidance for citizens on how to protect and improve Indiana’s water quality. By working together, we can make a difference!