Each year, thousands of illegal immigrants sneak across the border between Tijuana and San Ysidro, Calif.
A thin metal border fence helps separate the United States from Mexico and has helped stem the flow of immigrants but it's not enough. Now, the U.S. Border Patrol is trying to finish building a second fence but the effort is being blocked by the California Coastal Commission (search) because of environmental concerns.
In 2001, 12 million illegal aliens were arrested on the U.S.-Mexico border. Today, almost 9,000 border agents patrol the divide -- a huge boost from the 3,400 that watched over the area in 1993.
After Congress enacted the Immigration Reform and Immigrant Responsibility Act of 1996 (search), the government began building the 14-foot-tall second fence with 150-foot patrol roads on both sides and a third fence to further delineate the border security zone, reports the San Diego Union-Tribune. The secondary fence, which tilts forward at the top, is made of a special wire mesh with holes too small for even an ice pick or screwdriver to fit through.
The main fence was rebuilt in the early 1990s using metal runway mats from the military, the Union-Tribune reported. It averages about 10 feet in height.
A nine-mile section of the new fence has already been built and although it doesn't stop everyone, it gives border agents enough time to catch most who try to sneak into the United States. The final three miles, which run right up to the Pacific Ocean, are currently wide open.
Much of the environmental concern stems from the Border Patrol’s plans to fill a deep, half-mile long canyon known as "Smuggler’s Gulch," (search) with 2.1 million cubic yards of dirt, enough to fill 300,000 dump trucks. As much as 800 feet of the new fence is proposed to cross the gulch.
The U.S. Fish and Wildlife Service also opposed filling in Smuggler’s Gulch.
The state coastal commission, which controls development along California's coastline, also claims the fence will damage or threaten the Tijuana estuary, which runs along the border between California and Mexico and serves as a refuge for threatened birds.
The commission last month voted the final three-mile project down and sued to stop continuation of the project.
"We only look at whether a project complies with the environmental laws," said Scott Peters of the coastal commission. "We have people testify to us about national security, on the other side about human rights, that's really not what the basis of our decision is."
But the Border Patrol (search) agents and some U.S. lawmakers say it should be and they warn that an open border is a greater threat to national security.
"If you look at the list of people who have crossed that piece of the border in the last several years there are a ton of people that come from terrorist nations and from states that back terrorism," said Rep. Duncan Hunter, R-Calif., a member of the House Armed Services Committee.
Besides the national security issue, the Border Patrol claims a new fence will actually help preserve the estuary.
Right now, without the fence to protect the area, illegals are trampling native plants, leaving trash all over the environmentally sensitive area and even cutting down brush to start fires to keep warm at night.
The San Diego Audubon Society, Sierra Club, the California Native Plant Society, Southwest Wetlands Interpretive Association, San Diego BayKeeper and the Center for Biological Diversity support the coastal commission's lawsuit.
The coastal commission ruling could delay the final phase of the $58 million project. If the two sides can't reach a compromise, the issue is likely to land in federal court.
But the U.S. government holds the ultimate trump card: The president can override the court on grounds of national security.
Click here for a complete report by Fox News' Adam Housley.