The San Pedro's riverbed was a wildlife superhighway. Every trip down I'd see tracks across the border. No, not from migrants or smugglers, but from foxes, bobcats, mountain lions & coatimundi. The wall will now stop these species dead in their tracks.

Before/after construction:

The wall has decimated the river's floodplain. When monsoons come, floods smash through this often-dry region, sometimes topping 10,000 CFS. That's more water than the Colorado (or similar to the Potomac for you east-coasters). This wall will choke the river to death.

It's also a serious threat to public safety. Landowners fear floodwaters could back up behind the wall, causing immense pressure & leading to collapse. A tidal wave of water could rip into the U.S. destroying property, endangering lives & wiping out wildlife habitat.