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Contact EPA Pacific Southwest Water Division

Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

EMAP Western Pilot

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Western EMAP

Surface Waters

The surface water component of the EPA Environmental Monitoring and Assessment Program (EMAP) Western Pilot was a multi-year effort to assess the ecological condition of rivers and streams across 12 states in the western United States. EMAP is designed to monitor indicators of pollutant exposure and habitat condition and seek associations between human-related stressors and ecological condition. A probability-based survey design was employed in which sites are randomly selected to eliminate potential bias and to make estimates of condition over defined geographical areas.

In EPA Region 9, EMAP sampled perennial streams in Arizona, California, Nevada and selected tribal areas for four years to produce statewide estimates of condition. Approximately 50 sites per state were monitored to provide the statewide estimates. Additional monitoring effort occurred in two intensive study areas in California. These two intensive study areas were the coastal watersheds in northern California, from the Oregon border to Tomales Bay, and in southern California, from Point Conception to the Mexican border. Approximately 80 samples were allocated to each of the two intensive study areas.

Surface waters indicators

Biological, physical habitat, and water chemistry indicators provide measurements of the environment by characterizing the habitat attribute and/or quantifying the level of stress. Indicators to be measured are divided into three tiers: Tier 1 indicators are the core indicators, which were completed at all sites; Tier 2 and 3 indicators were measured at a subset of sites depending on local importance and resource availability.

Tier 1 (Core) Tier 2 Tier 3
Water quality parameters
Fish assemblage
Macroinvertebrate assemblage
Periphyton assemblage
Physical habitat structure
Riparian vegetation
Fish tissue chemistry/toxics
Sediment metabolism
Sediment chemistry
Riparian birds


Site evaluations took place in fall 1999. Field sampling began in the spring/summer 2000 and continued through 2004. Prior to each year's field sampling, sites were reviewed for sampleability, ownership and physical access status.


  • Estimates of condition for wadeable streams on a state level and for intensive study areas
  • Estimates of the % stream miles having desirable/good condition
  • Support biocriteria development (using biological indicators for standards development)
  • Strengthening of statewide water-quality and biological assessments
  • Identification of potential reference conditions

EPA strongly supports partnerships with public and private stakeholders. Partners are encouraged to participate by providing site access information, supplementing the monitoring effort (i.e., add other indicators or sample analyses), contributing financial or staff resources, and supplying input and feedback during data analysis.

Further information

Janet Hashimoto (hashimoto.janet@epa.gov)
(415) 972-3452


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