Department of
Environmental Quality

Idaho's Water Quality Standards prescribe certain criteria that must be met to ensure the beneficial uses of the state's surface waters are supported. These criteria can be numeric (parameter-specific) or narrative. Numeric criteria are use-specific, while narrative criteria are general, applying to all waters irrespective of use. Together, the numeric and narrative criteria must contain sufficient parameters or constituents to protect the designated use.

Common Water Quality Measures

Some of the most common measures of water quality are ammonia, bacteria, dissolved oxygen, nutrients, pH, sediment, temperature, toxic substances, and turbidity. Each is important to the health or utility of a water body. Learn more.

Numeric Water Quality Criteria

Individual numeric criteria are based on specific data and scientific assessment of adverse effects. Numeric guidelines assign numbers that represent limits and/or ranges of chemical concentrations, like oxygen, or physical conditions, like water temperature. Learn more.

Narrative Water Quality Criteria

To supplement numeric criteria, Idaho has adopted narrative criteria. Such narrative criteria are statements that describe the desired water quality goal, such as Idaho's waters being "free from" pollutants. Learn more.

Site-Specific Water Quality Criteria

In some cases, it may be prudent in some water bodies to develop new water quality criteria or modify existing criteria through site-specific analyses that will effectively protect designated and existing beneficial uses. Learn more.

Toxic Criteria

A toxic substance is any substance, material, or disease-causing agent, which upon exposure, ingestion, inhalation, or assimilation into an organism will cause death, disease, malignancy, physical deformations, or other abnormalities in affected organisms or their offspring. Toxic criteria exist for the protection of aquatic life and human health. Learn more.