Bioassessment and Biocriteria Program Status for Arizona: Streams and Wadeable Rivers

Related Information

Information on Bioassessment and Biocriteria Programs for Streams and Wadeable Rivers

State Program Contact

Arizona Department of Environmental Quality

Water Quality Standards

WQS Information

The link to Arizona's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by the U.S. Environmental Protection Agency.

The state of Arizona provided information and links to sections of their administrative code on designated aquatic life use, biological criteria, antidegradation as well as technical support documents and information on its bioassessment and biocriteria programs. These are included for your convenience and may or may not reflect the most recently EPA-approved WQS.

Designated Aquatic Life Uses

Arizona has adopted narrative and numeric biocriteria to protect aquatic life uses in wadeable, perennial streams designated for either coldwater aquatic and wildlife (A&Wc) or warmwater aquatic and wildlife (A&Ww). Those biocriteria allow the state to define expected conditions relative to reference streams which have been characterized as least disturbed conditions.

Biological Criteria

__X__ Narrative statement
__X__ Numeric
_____ No criteria

Arizona Administrative Code R18-11-108(E)
R18-11-108.01 Narrative Biological Criteria (pdf)

A wadeable, perennial stream shall support and maintain a community of organisms having a taxa richness, species composition, tolerance, and functional organization comparable to that of a stream with reference conditions in Arizona.

  1. The narrative biological criteria in this Section apply to a wadeable, perennial stream with either an aquatic and wildlife (cold water) or an aquatic and wildlife (warm water) designated use.
  2. The biological standard in is met when a bioassessment result, as measured by the Arizona Index of Biological Integrity (IBI), for cold or warm water is:
    1. Greater than or equal to the 25th percentile of reference condition, or
    2. Greater than the 10th percentile of reference condition and less than the 25th percentile of reference condition and a verification bioassessment result is greater than or equal to the 25th percentile of reference condition.
  3. Arizona Index of Biological Integrity (IBI) scores
    1. Bioassessment Result
      1. Greater than or equal to the 25th percentile of reference condition
        1. A&Wc Index of Biological Integrity Scores ≥ 52
        2. A&Ww Index of Biological Integrity Scores ≥ 50
      2. Greater than the 10th and less than the 25th percentile of reference condition
        1. A&Wc Index of Biological Integrity Scores = 46 - 51
        2.  A&Wc Index of Biological Integrity Scores = 40 - 49

Antidegradation Policy

Antidegradation (pdf) criteria in WQS (R18-11-107.01) does not currently include a bioassessment methodology
Implementation procedures for Antidegradation

Biological Assessment

What biological assemblages are used in the bioassessment program?
Benthic macroinvertebrates and benthic diatoms

Are bioassessments used to support 303(d) listings?
No. Listing Methodology: ADEQ needs to have the 303d listing criteria included in the Impaired Waters Identification Rule (IWIR) prior to listing streams with impaired IBI Score. The Rules moratorium in AZ is preventing this.

How are assemblages used to make impairment decisions?
AZDEQ cannot yet make impairment decisions based on macroinvertebrate bioassessments. When the IWIR is updated, bioassessments can then be used to list impaired streams. AZDEQ has two multimetric IBIs for warm and coldwater stream macroinvertebrate communities and is developing a periphyton (diatom) bioassessment tool. It’s anticipated that the two assemblage indexes will be applied independently.

Other uses of biocriteria or bioassessment within the water quality program:
Support antidegradation policies, 305(b) surface water condition assessments, BMP evaluation, and criteria development

Technical Support Information and Documents

Reference condition

Arizona’s narrative biocriteria statement in the Surface Water Quality Standards reflects the biological integrity goal of the Clean Water Act: “A wadeable, perennial stream shall support and maintain a community of organisms having a taxa richness, species composition, tolerance, and functional organization comparable to that of a stream with reference conditions in Arizona.”[A.A.C. R18-11-108(E)]

ADEQ defines “reference condition” in the surface water quality rules at A.A.C. R18-11-101(36) as “a set of abiotic physical stream habitat, water quality, and site selection criteria established by the Director that describe the typical characteristics of stream sites in a region that are least disturbed by environmental stressors. Reference biological assemblages of macroinvertebrates and algae are collected from these reference condition streams for calculating the Arizona Indexes of Biological Integrity thresholds. Streams must meet the following criteria to be considered “reference.”

  • No known discharges upstream
  • No major impoundments upstream
  • No channel alterations at the site
  • Located >0.5 km downstream of road crossings
  • Site should be free of local land use impacts
  • Site should be truly perennial (presence of fish, univoltine insects, riparian indicators)
  • No violations of pH or dissolved oxygen water quality standards
  • ADEQ Habitat score > 14
  • Accessible (within a 2-hour hike or 3-4 mi from nearest road)
A statewide reference site monitoring network was established in 1992 to develop datasets for development of the indexes of biological integrity as the macroinvertebrate bioassessment tool, and reference site monitoring continues annually.

Technical reference material

Biocriteria

ADEQ has developed procedures for macroinvertebrate sample collection in perennial, wadeable streams and for laboratory processing and taxonomic identification for purposes of conducting bioassessments to evaluate biological integrity in perennial streams of Arizona. These SOPs are documented in ADEQ’s Standard operating procedures for surface water quality sampling (ADEQ, 2018) and in the Biocriteria Program Quality Assurance Program Plan (ADEQ, 2006). A statewide reference site monitoring network was established to develop datasets for development of the indexes of biological integrity as the macroinvertebrate bioassessment tool, and reference site monitoring continues annually.

Bioassessment tools (the indexes of biological integrity) were developed following the EPA's Rapid Bioassessment Protocols documents (EPA, 1999). Before the tools were created, a classification of stream and macroinvertebrate community types was required. ADEQ conducted a classification analysis on the statewide macroinvertebrate datasets, identifying cold (>5000’ elevation) and warm (<5000’) regions for which to develop bioassessment tools (Spindler, 2001). All wadeable, non-effluent dependent, perennial streams located in these regions are predicted to have the same general macroinvertebrate community type. Indexes of Biological Integrity (IBI) were then developed for both a warm water community and a coldwater community type, using Arizona’s statewide network of reference site data (Gerritsen and Leppo, 2000; Leppo and Gerritsen, 2001). Background information about reference conditions and the development of the IBIs is presented in the Biocriteria Technical Support document (ADEQ, 2007).  The numeric targets for biocriteria and associated applicability rules are listed in R18-11-108.01. The biocriteria standard overall consists of the narrative biocriterion, statement of applicability, rules explaining how the biocriterion is met, and associated IBI scores for cold and warm water streams. Details on the Biocriteria standard and its applicability are provided as technical reference material in the ADEQ Implementation Procedures for the Narrative Biocriteria Standard (ADEQ, 2015).

Technical reference material

Stressor identification/causal analysis approach

A stressor identification approach process is under development at ADEQ, to help identify causal pollutants/stressors for an impaired bioassessment result. TetraTech developed a Causal Assessment Screening Tool (CAST) to assist ADEQ with initial screening of stressors for a stream reach.

Technical reference material

Lincoln, A. 2019. AZDEQ Causal Assessment Screening Tool. TetraTech, Owings Mills, MD.

Water Quality Criteria

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Last updated on June 4, 2025