US-Mexico Border: No border crossing allowed in Big Bend National Park.

NPS/Sharon Collyer
The former Boquillas crossing remains closed

Crossings Remain Closed

"As a result of a 2002 US Customs and Border Protection decision, there are NO authorized crossings in Big Bend National Park. Crossing at Boquillas, Santa Elena, or other locations along the Rio Grande is prohibited. The closest legal ports of entry are Del Rio and Presidio, Texas.
The U.S. Attorney’s Office has indicated that it will prosecute any criminal violations regarding any illegal crossings. If you re-enter the United States at any point within Big Bend National Park, you may be liable for a fine of not more than $5,000 or imprisonment for up to one year, or both. "
Big Bend National Park Website

More information:

The U.S. Border Patrol also mans checkpoints on the highways leading to Big Bend National Park. The National Park Service has provided information on border crossings, legalities and how both U.S. citizens and foreign nationals can avoid trouble.

Click here for the "Visiting a Border Area" section of the Big Bend National Park website.