Protect Arizona's Waters

Before the Trump Administration changed the definition of Waters of the United States (WOTUS) in 2020 to exclude temporary (intermittent and ephemeral) waters, they were federally protected. We are asking the State of Arizona to renew protection for these waters. Why is it necessary to do so?

Let’s begin with some definitions. Perennial waters, like the Colorado River, flow continuously. Intermittent waters flow on the surface only at certain times of year (such as after snowmelt), and ephemeral waters flow on the surface in direct response to precipitation. Many temporary waters are tributaries that empty into perennial rivers.

Nearly all of Arizona’s waters are either intermittent or ephemeral—94 percent, to be exact. Many perennial waters in the arid southwest are or may soon become intermittent or ephemeral waterways in response to environmental stressors. Climate change is raising temperatures, decreasing precipitation and increasing the length of droughts. Excessive groundwater pumping for new housing developments, agriculture, and mining also contributes to the drying of our rivers. As Arizona may soon lose a significant portion of the Colorado River water (CAP) it depends on, a decision to leave most of Arizona’s fresh waters unprotected is extremely short sighted.

The health of perennial rivers that still flow in arid regions is improved by the transport of water and sediments from intermittent and ephemeral streams. For example, water from monsoonal rains flowing in ephemeral tributaries can replenish regional groundwater aquifers of perennial rivers. As groundwater accounts for forty percent of the water Arizona uses, replenishing aquifers is crucial for sustainable water use.

Beyond keeping our perennial rivers healthy and recharging groundwater aquifers, intermittent and ephemeral streams perform crucial biological functions in arid regions. In Arizona, it is easy to pinpoint the location of these temporary waters—just look for the ribbons of green hugging their banks. These green “riparian” areas are home to a vast number wildlife species because they are cooler, contain more trees and greater plant diversity, provide cover, nesting and breeding habitat, and offer diverse sources of nutrition. Riparian corridors also provide safer pathways for dispersing resident and migrating wildlife in an otherwise harsh landscape. Unprotected, these waterways will likely disappear or become contaminated, resulting in the loss of multiple species. In particular, many amphibians and most of our native fish rely on permanent pools in otherwise dry reaches of intermittent or ephemeral streams. Ninety-five percent of riparian areas have already been lost in the arid southwest. We can’t afford to lose more.

Because ephemeral and intermittent waterways are no longer federally protected, it is up to state governments to enact legislation to protect them. In a state like Arizona, with so few perennial waters, the importance of these temporary waterways must be recognized and a proactive strategy established for their sustainable management. We must act now to protect Arizona’s water, our scarcest and most precious resource, for ourselves, our children, and our wildlife.


Creed, I.F., C.R. Lane, J.N. Serran, et al. 2017. Enhancing protection for vulnerable waters. Nature Geoscience 10:809-815.

Goodrich, D.C., W.G. Kepner, L.R. Levick, et al. 2018. Southwestern intermittent and ephemeral stream connectivity. Journal of the American Water Resources Association 54:400-422.

Levick, L.R., J. Fonseca, D.C. Goodrich, et al. 2008. The ecological and hydrological significance of ephemeral and intermittent streams in the arid and semi-arid American Southwest. U.S. Environmental Protection Agency and USDA/ARS Southwest Watershed Research Center, EPA/600/R-08/134, ARS/233046. 116 pp.

USEPA (U.S. Environmental Protection Agency). 2015. “Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence. EPA/600-R-14/475F, 408 pp. 296414.