An official with the U.S. Fish and Wildlife Service (USFWS) told NPR in an article published Tuesday that the agency is working with Border Patrol officials to make sure President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's signature border wall doesn't endanger local animal species that could be trapped by potential flooding.

The unnamed spokesperson said USFWS is working with Customs and Border Protection (CBP) “to construct large aprons around all future gates along new levee border wall to create areas where wildlife can escape rising water during flood events."

Environmental groups and animal advocates are among those who have filed legal challenges to President Trump’s border wall, arguing it could harm ecosystems and endangered species.

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"Can we design it so that it is not as impactful, to develop like a passage corridor? I'll be honest, those are some challenges that are happening along the whole entire southwest border where we're putting in wall," Carmen Qualia, an assistant chief with Border Patrol in the Rio Grande Valley, told NPR.

The USFWS does not officially oppose border wall construction.

Ken Merritt, a former USFWS manager of the refuges in South Texas, said agency employees are limited in how much they can speak out on projects that may affect the parks they manage.

"A lot of them are worried about their careers," Merritt says. "I think most of them have been told not to say a word."

The land along the Texas border, the longest stretch of the U.S. that touches Mexico, is mostly privately owned, meaning litigation between each property owner needs to be settled before construction can begin.

One way the administration has gotten ahead on border wall construction is by beginning in federally owned property, such as Santa Ana National Wildlife Refuge in Alamo, Texas.

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Congress has attempted to protect environmentally sensitive areas in the appropriations bills that fund border wall construction.

The 2019 appropriations bill included language put in by Democratic Texas Reps. Henry Cuellar, Vicente Gonzalez and Filemon Vela Filemon Bartolome VelaHispanic Caucus asks for Department of Labor meeting on COVID in meatpacking plants The Hill's Campaign Report: Biden builds big lead in battleground Florida Texas Democrat proposes COVID-19 victims' compensation fund MORE, instructing CBP not to build the wall in Santa Ana and other neighboring nature parks.

Since then, border wall funding has continued to be a major dispute in appropriations negotiations.

The Washington Post reported Monday that Trump plans to divert another $7.2 billion in defense funding to go toward border wall construction, five times more than what Congress authorized in its budget.

Trump has promised 450 miles of new border barriers will be completed by the end of the year, with 101 miles completed so far.

—Updated Thursday at 10:27 a.m.