Illegal immigrants "degrade the environment," according to Homeland Security Sec. Michael Chertoff, speaking to the Associated Press.

"Illegal migrants really degrade the environment. I've seen pictures of human waste, garbage, discarded bottles and other human artifact in pristine areas," Chertoff told the AP. "And believe me, that is the worst thing you can do to the environment."

Chertoff was defending the need for a "virtual fence" on the border between the United States and Mexico, which he implied would be an environmental boon in border areas. Some opponents say such barriers are harmful to the environment.

Over 150 miles of fence had been constructed through last week, Chertoff said, less than half of the 370 miles of actual fencing Homeland Security hopes to construct.

-Michael O'Brien