Nightline E-mail: August 20

W A S H I N G T O N, August 20 -- People go to where the money is; always have - probably always will. Whether we're talking about the California Gold Rush or today's global immigration trends, it's a natural survival instinct. People need to work, they need to feed their families. But when a lot of people go in the same direction, chaos can ensue.

Since the passage of the North American Free Trade Agreement in 1994,known as NAFTA, life along the U.S. - Mexican border has dramatically altered. Many consider this area the new frontier of economic growth, international cooperation and commercial expansion. But consider the negatives as well.

Over 400 U.S.-owned factories have sprouted along the Mexican side of the border in recent years. These factories, known in Spanish as maquiladoras, enable U.S. firms to hire cheap Mexican labor to create low-priced goods for sale on both sides of the border. Thousands of workers are needed to make those maquiladoras hum. So, thousands of Mexicans have abandoned the relative economic bleakness of the villages of internal Mexico and sought employment along the border.

Life in Juarez, Mexico has, of course, changed by the arrival of these factories and the thousands of Mexicans seeking employment in them. Today it is a city of 1.3 million people - thousands living in its newest and ever expanding slums. The infrastructure, never particularly modern, has been overloaded, as the new arrivals put increasing pressure on the water, sewage and other government-run systems.

But on the other side of the border, in El Paso, Texas, life has undeniably shifted as well. The pollution that clogs Juarez' air and water, cannot be kept out of El Paso. A health care crisis, like a rampant virus or bacterial infection, exacerbated by the unclean living conditions, will no doubt bring illness to people on both side of the border.

Keep in mind that if NAFTA is to expand and succeed the way its supporters intend, more cities along the border will start looking like Juarez and El Paso. If these problems are not addressed there, we are bound to see them repeated elsewhere.