PALOMINAS, Ariz. - Before sealing off the border became the priority it is today, a visitor would have gotten a different picture of this area where the last free-flowing river in the Southwest trickles between tree-lined banks.
The San Pedro River still moves lazily northward below a canopy of willows and cottonwoods. But on a recent day, a bulldozer mounding dirt only 50 yards from its elevated eastern bank in preparation for the advance of a border fence presented a stark contrast to its serenity.
The federal government contends the fence is needed to stem the flow of illegal immigrants and drug-runners through the area. Environmentalists say it may slow some illegal crossers but will have a devastating impact on wildlife and the environment in the riparian area that encompasses the river.
Mountain lions, jaguars, white-tailed deer, black bears and some ground birds will be among wildlife especially affected by the fence, which is just some 400 yards from the river at this point, said Matt Clark, a spokesman for Defenders of Wildlife.
"When you construct a barrier across a conservation habitat, you're limiting the ability of a species to find food, habitat and mates, and you're preventing genetic exchange between populations," Clark said.
Clearing of habitat for the construction also will affect the river's hydrology, increasing erosion and sedimentation, possibly destabilizing the river's banks and potentially shifting its course, which would impact its canopy of trees, he added.
Environmental issues have been raised along other portions of the U.S.-Mexico border tabbed for fencing as well, including south Texas and San Diego.
In southern Arizona's San Pedro Riparian National Conservation Area, they led to a judge's order that halted construction until Homeland Security Secretary Michael Chertoff waived 19 environmental, conservation and cultural laws in late October.
The judge had criticized Homeland Security and the Bureau of Land Management for taking only three weeks to conduct a biological assessment, which also allowed for no public input. Environmentalists said a more in-depth environmental study was needed first - the very approach that Chertoff was following before fence-building in Texas.
Chertoff now has invoked the waiver power a total of three times to continue border fence construction, drawing the ire of environmental advocates each time.
Russell Knocke, a spokesman for Chertoff, said he rejects the allegations that the fence building will devastate the San Pedro's ecology.
Knocke said critics omit the reality of the situation, where abandoned vehicles and trash - from plastic water bottles to food containers, clothing and human waste - scar the same area.
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"Environmental experts and common sense tells you that border infrastructure is far more likely to have a positive contribution to the environment in this area over the long run," he said.
Chris Paolino, a spokesman for the Department of the Interior, said the Bureau of Land Management, which manages this area, completed an environmental assessment on the general goals of the fence and concluded it would have no significant environmental impact.
More than 70 miles of primary fencing costing $3 million a mile have been built in Arizona, where more illegal entries occur than any other state on the Mexican border.
Congress authorized construction of 700 miles along the international boundary, and Homeland Security has promised to complete some 370 miles of vertical steel walls by the end of 2008.
What makes the issue of the fence in the San Pedro River area so compelling for environmentalists is what makes the river so special - and what prompted Congress to designate it as the first-of-its kind San Pedro Riparian National Conservation Area in 1988.
The San Pedro is a vital desert oasis for millions of birds - more than 150 species of breeding birds and more than 250 more species that migrate and winter along the river. That makes up about half of all known breeding species identified in North America. It has diverse plant and animal populations as well.
Threatened and endangered species include the jaguar, the lesser long-nosed bat and the southwestern willow flycatcher.
Bill Odle, a retiree who lives a few hundred yards north of an existing portion of the fence, said small and large critters alike - like a porcupine he watched one day - find themselves stymied when confronted by the mesh fence.
Meanwhile, illegal immigrants or drug-runners have cut more barbed wire on a ranch adjacent to his land since fencing began in September, he said.
"We need border security, but you don't do that by putting up a wall that stops nothing but wildlife," Odle said.
Knocke said federal officials take environmental issues seriously.
"When weighing the safety of a lizard with the protection of a human being, the choice is painstakingly obvious," he added. "The methamphetamine that could otherwise be smuggled through that very area absent that border structure will ultimately jeopardize the health and safety of an adult or child somewhere else in America."
© 2007 Associated Press