Illegal immigration is something that, despite the combined efforts of the U.S. Customs and Border Protection and various law enforcement agencies, cannot be totally prevented. Attempts to stem the flow of illegal immigrants have only slowed the illegal crossings to some degree. Most of the immigrants in the U.S. come legally, but there can be dangerous consequences for those who try to get into the country illegally.
Many illegal immigrants simply overstay after entering the country legally, but for those who cannot get a visa, they will search for other ways to enter the United States. Those who live south of the border often trek for hundreds of miles across the desert in order to make it to the U.S., and risk dying of exposure, starvation, or dehydration. Desert wildlife such as rattlesnakes, tarantulas, scorpions, and even wild coyotes can also harm them.