Nearly 90 miles of recently funded border wall and its accompanying enforcement zone likely will run through more than 13,000 acres of federally protected wildlife refuge lands along the Rio Grande, according to U.S. government communications obtained by the American-Statesman.

The acreage represents about 15 percent of the Lower Rio Grande Valley National Wildlife Refuge, a series of protected parcels that the U.S. Fish and Wildlife Service, private donors and environmental groups have spent more than $75 million to carve out of the rapidly urbanizing Rio Grande Valley over the past four decades.

Home to one of the most biologically diverse regions in North America, the refuge protects some of the last vestiges of native Tamaulipan thornscrub habitat in the Rio Grande Valley and supports hundreds of often rare species of migratory birds, butterflies, reptiles and potentially endangered wildcats.

The refuge stretches across 275 miles of riverfront land from the Gulf of Mexico to Falcon Lake in more than 140 individual tracts over almost 100,000 acres. While some tracts have little public access, the refuge maintains more than 40,000 acres for wildlife watching and hiking and another 6,000 acres for hunting.

Under a budget deal reached earlier this year, Congress funded 55 miles of border fencing in the Rio Grande Valley, in addition to 33 miles approved last year. The deal exempted environmentally sensitive areas like Bentsen-Rio Grande Valley State Park, the National Butterfly Center, the Santa Ana National Wildlife Refuge and La Lomita chapel but not the Lower Rio Grande Valley refuge. A national emergency declared by President Donald Trump to access additional border wall funds could remove protections for those sites. Official locations of the most recently funded border fencing have not been publicly announced.

According to an internal calculation by the U.S. Fish and Wildlife Service, the new fencing likely will run through 12 refuge tracts in Hidalgo County and another ten tracts in Starr County, further upriver, which would affect 13,832 acres of Lower Rio Grande Valley refuge lands.

The agency referred questions about wall construction on its refuge to U.S. Customs and Border Protection, which did not immediately respond.

The impact of the new sections of border wall will be far greater than during the previous round of border barrier construction a decade ago, when the Department of Homeland Security built 55 miles of border fence in Hidalgo and Cameron counties, including segments that blocked or bisected several refuge tracts. Back then, authorities included anywhere from 20 to 60 feet of enforcement zone south of the fence.

This time, border officials are planning to build an enforcement zone of 150 feet for roads and lighting structures, resulting in significantly more vegetation loss, wildlife agency officials said.

The wildlife agency has long declined to discuss effects of the border wall publicly, but behind the scenes, officials have warned for more than a decade that the border wall could lead to “serious, and likely irreparable, wildlife and habitat loss and damage” and undo efforts to rehabilitate the refuge, which was created in 1979.

Construction has already begun on a tract just west of Bentsen-Rio Grande Valley State Park, and critics of the wall say U.S. Customs and Border Protection is targeting the refuge first because it is federally owned and doesn’t require what can be lengthy condemnation proceedings of private land.

“It shows that the walls are not being built for tactical considerations but for ease of construction,” said Scott Nicol, co-chair of the Sierra Club's Borderlands Campaign.

Environmental groups worry the planned border fencing and enforcement zones will have a disastrous effect on the refuge’s stated goal of preserving wildlife habitat, especially if the Department of Homeland Security waives environmental rules along the fence's route as it has done throughout the border.

“Fifteen percent is pretty shocking,” Nicol said. “It’s hard to see it being functional.”

“It’s going to destroy the refuge system,” said Paul Sanchez-Navarro, senior Texas representative for Defenders of Wildlife. “They are basically throwing away a lot of tax dollars. What’s the plan to restore or remake the wildlife refuge?”

During the previous round of fence building in the Rio Grande Valley, federal officials set aside mitigation funding to purchase and restore protected land erased by the border fence. Though Customs and Border Protection originally agreed to spend $50 million in mitigation funds, less than $18 million was spent, including $2 million to help U.S. Fish and Wildlife add 500 acres to the Lower Rio Grande Valley National Wildlife Refuge. Environmental groups are seeking additional mitigation funding this time as well.

The Fish and Wildlife Service has long advocated for alternatives to a physical barrier across refuge lands. In a 2017 letter to U.S. Customs and Border Protection, it recommended that the border agency consider “technology, additional border patrol agents and other mechanisms, when possible, instead of the installation of levee or bollard walls” that would disrupt the movement of wildlife.

Fish and Wildlife also recommended minimizing the 150-foot enforcement zone, which it said will “create barriers and restrict wildlife movement, especially for species such as ocelots, which require dense brush to travel through.”

Recovery of the endangered ocelot has been a primary driver of refuge creation, though it has been many years since ocelots were witnessed crossing the Rio Grande, and some experts believe the wildcat’s best chance for survival is increasing habitat in less urbanized areas in the northern part of the Rio Grande Valley.

Fish and Wildlife officials also warned that the border wall would affect the flow of tourists, who it said contribute more than $10 million annually to the regional economy. The refuge includes “habitats that are harboring unique species of plants and animals, making the area a destination for ecotourists,” officials said.