The construction of former President Donald Trumps wall along the U.S.-Mexico border desecrated Indigenous cultural sites, hurt wildlife, destroyed vegetation, dried up key water resources, exacerbated the risk of flooding and triggered erosion that has left mountain slopes unstable and at risk of collapse, according to a new report.

The Government Accountability Office, a nonpartisan government watchdog, reviewed federal data and interviewed government officials, Native American tribes and stakeholders over the course of two years. The result is a comprehensive look at the widespread cultural and environmental harm much of which experts had predicted that came from Trumps relentless pursuit of what he called a big, beautiful wall along the southern U.S. border.

The Trump administration spent an estimated $15 billion constructing more than 400 miles of border wall, much of which replaced smaller existing barriers. It waived numerous environmental laws along the way. Trump had insisted during his campaign that Mexico would foot the bill for the construction, but Mexico never paid a dime.

Laiken Jordahl, a conservation advocate at the left-leaning Center for Biological Diversity who documents environmental damage in the borderlands, told HuffPost the report confirms all our worst fears about the damage wall construction has inflicted on wildlife, public lands and cultural resources.

Among other things, construction of the wall fragmented wildlife habitats, cut off species migration routes and destroyed ancient cacti and other native vegetation.

These border walls havent done a thing to address immigration or smuggling, but they did drive endangered species closer to extinction, butcher thousands of iconic saguaro cacti and dynamite Indigenous sacred sites and burial grounds, Jordahl said. This is a clear warning that any attempt to build additional miles of border walls would be a horrifically destructive and useless folly.