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Contact EPA Pacific Southwest Water Division

Pacific Southwest, Region 9

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

Watershed Priorities

photo of:
Santa Cruz River
Map of Santa Cruz Watershed Plan Template
Larger map | PDF version (1 pg, 381K)
Upper Santa Cruz River Riparian Vegetation Map, Santa Cruz County (PDF) (2 pp, 632K)

Santa Cruz Watershed, Arizona

On this page:

The Santa Cruz Watershed is defined as the drainage area of land that captures and transports surface and ground water within the basin. Some of the surface water sources in the Santa Cruz Watershed includes: Santa Cruz River, Sonoita Creek, Cienega Creek, Davidson Canyon, Harshaw Creek, Three "R" Canyon, Alum Gulch, Arivaca Lake, Parker Lake, and Lakeside Lake.

The Santa Cruz River has its headwaters in Arizona’s San Rafael Valley, which is in the south central part of the state. The river flows south and makes a 25-mile loop through Mexico before returning to U.S. soil about 5 miles east of Nogales, Arizona. The river then flows north from the U.S.-Mexican border up to its confluence with the Gila River, just southwest of Phoenix.

Most of the population in the Santa Cruz Watershed is found in the city of Tucson (population 530,000), the state’s second largest city. There is also a population of 370,000 located on the US-Mexico border in the sister border cities of Nogales, Sonora, Mexico and Nogales, Arizona. Grazing and irrigated crop production are the main land uses. Much of the agricultural land has been converted to urban use or retired. Mining is scattered across the watershed. The watershed includes eight designated wilderness areas, along with National Forests and National Parks with restricted land uses.

The Santa Cruz Watershed covers approximately 8,000 square miles, representing about 10% of the state of Arizona.

Watershed Implementation Activities

Border Activity

Since its inception in 1996, EPA's U.S.-Mexico Border Facilities Construction Program has committed funding to the planning/development/construction of four major projects in the Santa Cruz River watershed. EPA has provided $59.5 million for the upgrade of the Nogales International Wastewater Treatment Plant (NIWTP). This facility, which treats more than 14 million gallons per day (mgd) of wastewater from both Nogales, Arizona and Sonora and discharges it to the Santa Cruz River, is currently being improved to reduce contaminant loads of total nitrogen (including toxic loads of ammonia) and total suspended solids. Completion of the NIWTP upgrade is projected for the summer of 2009.  EPA also supports projects to improve wastewater collection system infrastructure in both Nogales, AZ and SN, including projects that will provide new wastewater service connections to more than 35,000 users who currently discharge raw sewage to the environment and ultimately to the Santa Cruz.

Information on Nogales projects is available on the BECC and NADB websites. Also, environmental information (Environmental Assessments and Finding of No Significant Impact) are available for review on EPA's Border website.


    (Watershed Assessment, Tracking & Environmental ResultS) unites water quality information from several independent and unconnected databases.
  • STORET Data for Upper Santa Cruz
    STORET (short for STOrage and RETrieval) is a repository for water quality, biological, and physical data and is used by state environmental agencies, EPA and other federal agencies, universities, private citizens, and many others.

Planning Documents

This watershed is currently impaired for the following pollutants:

  • Ammonia
  • Chlorine
  • Chlorophyll
  • Copper
  • Dissolved Oxygen
  • Escherichia coli bacteria
  • Mercury
  • Nitrogen
  • Low pH
  • Phosphorus
  • Zinc


All Partner links exit EPA.gov  Exiting EPA (disclaimer)


  • EPA's Watershed Central
    Watershed Central has been designed to assist users to develop and implement effective watershed management programs. The site includes guidance, tools, case studies, and data sets to help you share information, analyze data, and identify opportunities to initiate or strengthen your watershed efforts.
  • EPA's Watershed Webcasts
    Watershed Academy Webcast Seminars

Contact Information

Jared Vollmer (Vollmer.Jared@epa.gov)
(415) 972-3447
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