https://phys.org/news/2018-07-scientists-us-mexico-border-wall-threatens.html

Physical barriers prevent or discourage animals from accessing food, water, mates and other critical resources by disrupting annual or seasonal migration and dispersal routes. Work on border walls, fences and related infrastructure, such as roads, fragments habitat, erodes soil, changes fire regimes and alters hydrological processes by causing floods, for example.

The potential for ecosystem damage was highlighted more than a decade ago, when the U.S. Congress passed the Real ID Act. The 2005 law gives the Department of Homeland Security (DHS) authority to waive any laws—including the Endangered Species Act and National Environmental Policy Act—that slow the wall's construction.