PHOENIX — A newly built segment of the southern Arizona border wall may bolster national security, but it will endanger one of the rarest desert fish in the U.S., according to the Center for Biological Diversity.

The Sonora chub in Arizona is one of only two populations of the species in the U.S. and is protected under the Endangered Species Act. The fish live in the California Gulch, a stream in the western portion of the Atascosa Highlands, a region consisting of three small mountain ranges along the international border just west of Nogales.

The newly built border wall and paved road have impeded the flow of the stream where the fish live, according to a report the center released Wednesday.

The desert fish, a minnow that grows up to 20 centimeters in length, also feeds off of many native food sources in the surrounding streams. Though its Arizona population has remained steady since its discovery in 1995, the Center for Biological Diversity is concerned new infrastructure will push the fish to the brink.

Krista Kemppinen, a senior scientist at the center, said new border infrastructure is cutting this population off from its lifeline in Sonora.

“Designating California Gulch as critical habitat is more urgent than ever to minimize other threats, such as by keeping cows out of the Sonora chub’s pools,” Kemppinen said in a press release.

She also shared ideas for steps federal authorities can take to balance border security with environmental preservation.

“It’s also imperative that carefully designed culverts be added to the new border infrastructure to allow at least some semblance of a natural streamflow and migration. If federal officials are serious about saving this fish, they need to act now,” Kemppinen said.

What progress is being made to protect the fish from the new Arizona border wall segment?

Time is of the essence because the U.S. Fish and Wildlife Service previously stated it would not act on a request to help preserve the fish’s habitat until 2027 at the earliest.

This announcement followed a 36-page petition submitted by the Center for Biological Diversity in March 2023.

Kemppinen said authorities should designate four miles of the fish’s native area in Arizona as critical habitat.

“The Sonora chub’s survival depends on being able to access scarce desert water on both sides of the border, exchange genetic material with nearby populations in Mexico, and bolster its populations with upstream migrations of fish from Sonora after droughts,” Kemppinen said. “The new construction makes all that impossible.”

Besides access to water, other threats to the Sonora chub include uranium mining, nearby livestock grazing and recreational activity like the creation of hiking trails.

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