Department of
Environmental Quality

With over 92,000 miles of rivers and streams and over 100 lakes and reservoirs, water is one of Idaho's most important resources. Our rivers, lakes, streams, and wetlands not only provide great natural beauty, they supply the water necessary for drinking, recreation, industry, agriculture, and aquatic life.

DEQ's Surface Water Program is responsible for assuring Idaho's streams, rivers, lakes, reservoirs, and wetlands meet their designated beneficial uses and Idaho water quality standards.

Continuing Planning Process

As the agency tasked with implementing the federal Clean Water Act in Idaho, DEQ is required by section 303(e) of the act to develop a Continuing Planning Process (CPP) that describes the ongoing processes and planning requirements of the state's water quality program. One tool DEQ uses to implement its water quality program is its Water Quality Management Plan. In essence, it is a compilation of the guidance and programs DEQ uses to implement the Clean Water Act. Learn more.

Water Quality Standards

DEQ uses water quality standards to know if it is doing its job to protect Idaho's water. A water quality standard defines the goals that have been set for a water body by designating the uses for the water, sets criteria necessary to protect those uses, and prevents degradation of water quality. Learn more.

• Natural Background Conditions
• Mixing Zones
• Variances from Idaho Water Quality Standards
• §401 Certification
• EPA Actions on Proposed Standards

Beneficial Uses

Designated beneficial uses are the desirable uses that water quality should support. Beneficial uses include drinking water supply, primary contact recreation (such as swimming), and aquatic life support. Each designated use has a unique set of water quality requirements or criteria that must be met for the use to be supported. A waterbody may have multiple beneficial uses. A waterbody is considered impaired when it does not attain the water quality standards needed to support its designated uses. Learn more.

Antidegradation Guidance Under Development

Antidegradation describes policies designed to maintain water quality even if it exceeds levels necessary to support beneficial uses. Federal water quality standards require Idaho to establish a three-tiered antidegradation program. Learn more.

Water Quality Criteria

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. Learn more.

• Common Water Quality Measures
• Numeric Water Quality Criteria
• Narrative Water Quality Criteria
• Site-Specific Water Quality Criteria
• Criteria for Toxic Substances

Mercury

Mercury is a naturally occurring metallic element that is found in trace amounts in air, water, and soil. Mercury is toxic to both aquatic life and humans, but its toxicity is primarily a human health concern. By far the most common route of mercury exposure in humans is eating fish contaminated by methylmercury, according to the federal Centers for Disease Control. Learn more about mercury in surface water and what DEQ is doing to address this contaminant here.

Temperature

Water temperature is a key factor in the health of fish and other coldwater organisms. Warm water can stress and even kill coldwater fish such as salmon and trout. Warm water can alsomake other water quality problems worse. For instance, it can lead to increased bacteria and nuisance aquatic plant growth and intensify water chemistry problems involving dissolved oxygen and pH. If stream temperatures are too high, other water quality problems may be present as well, such as eroding stream banks and excessive sedimentation. Idaho's water temperature standards are designed to protect aquatic life uses. Learn more.

Monitoring and Assessment

As the agency responsible for protecting Idaho's surface water, DEQ continually monitors and assesses the quality of the state's rivers, streams, and lakes. This information is used to report to the U.S. Environmental Protection Agency and to make decisions regarding water quality management. Learn more.

• Beneficial Use Reconnaissance Program
• Integrated Report
• Outside Data Policy
• Use Attainability Analysis

Nonpoint Source Pollution

Unlike pollution that is discharged directly from a pipe into surface waters, nonpoint source pollution generally does not have a single point of origin. NPS pollutants can be natural, such as sediment, or human-made, such as chemicals and toxics. They are generally created in or on the land and carried off by stormwater runoff when it rains or the snowpack melts. Nonpoint source pollution can damage fish, wildlife and their habitat, promote excessive weed growth, generate odors, and degrade Idaho's scenic beauty and recreational opportunities. Learn more.

• Idaho's Nonpoint Source Management Program

Total Maximum Daily Loads

When water bodies are found not to be meeting water quality standards, DEQ develops Total Maximum Daily Loads, or TMDLs, to improve water quality. A TMDL is a calculation of the maximum amount of a pollutant that a water body can receive from human-caused sources and still meet water quality standards. This budget is expressed in terms of loads: the amounts of pollutants added to a water body during a given time or per a volume of water. Learn more.

• Table of Subbasin Assessments, TMDLs, Implementation Plans, and Five-Year Reviews
• TMDL Implementation Plans
• Basin Advisory Groups
• Watershed Advisory Groups
• Frequently Asked Questions about Subbasin Assessments and TMDLs

Water Quality Studies & Reports

DEQ produces three major types of water quality reports and studies: Status Reports, Summary Reports, and Water Body-Specific scientific Studies. Learn more.

• DEQ Water Quality Status Reports
• DEQ Water Quality Summary Reports
• Water Body Studies & Plans