Rivers and Streams

The Santa Cruz River

illustration of river peaking out among trees illustration of river peaking out among trees

Left image
An artist's rendering of the Santa Cruz River among cottonwoods

Right image
Tumacácori's stretch of the Santa Cruz River


How It Was

The Santa Cruz River begins in the San Rafael Valley. It flows south into Sonora, Mexico and then makes a U-turn and flows north back into Arizona. The river continues to flow north through the Santa Cruz Valley, eventually emptying into the Gila River. Seasonal rainfall and cooler conditions allowed for yearlong water flow in the river. Throughout its course, the river reduced to seeps and springs, however water continued to flow underground. Drawn to the lush banks of the river, human settlements coincide with gaining reaches in the river. Communities such as Tumacácori, Guevavi, and Tubac persisted over hundreds of years at locations along the river where water was forced to the surface by high bedrock, providing a more reliable water source.


How It Is Now

Now an ephemeral stream throughout most of its stretch, the Santa Cruz riverbed is dry most of the year, except for occasional water flow following seasonal storms and floods. Water use over the last century has exceeded the aquifer's ability to recharge, resulting in decreased water levels in the water table and a dry river bed. Human disturbance can change the availability of water and nutrients, which in turn cause changes in the plant and animal communities. Among the most serious impacts to western river ecosystems are water diversion, groundwater pumping, livestock grazing, land clearing and development, the elimination of native species such as the beaver, and the introduction of non-native animals and plants such as the bullfrog and the tamarisk tree. The Santa Cruz River has been seriously impacted by many of these threats.

The stretch of the Santa Cruz River that winds through Tumacácori National Historical Park has been restored to perennial water flow due to discharge from the Nogales International Wastewater Treatment Plant several miles upstream. This discharge provides an otherwise unavailable year-round water supply, recharges the aquifer, and allows for the cottonwood-willow riparian habitat to persist.

The Santa Cruz supports the southwest cottonwood-willow riparian (streamside) environment, one of the most endangered ecosystems in the United States. A “riparian” area is the lush corridor of water – loving plants growing along the banks of a river. These ecosystems are essential habitat for many plants, birds, and other animals which could not otherwise live in the surrounding desert and scrub environments.

Important Health and Safety Note

The flow in the Santa Cruz River between Rio Rico and Tubac consists almost completely of effluent released from the Nogales International Wastewater Treatment Facility.

For your health and safety:
- Avoid contact with the river water.
- Do not drink or wash with the water.
- If you come into contact with river water, wash the affected area as soon as possible.


Science of the Santa Cruz River

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    Last updated: July 23, 2020

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