The plans were unveiled in the first detailed look at the Wall the government says it must build to slow illegal immigration along the 1,200-mile-long (1,920-km) Texas-Mexico border. In a request for public comment on the environmental impact of the Wall, the U.S. Customs and Border Protection agency said construction could begin next spring

South of Texas

The fence, to be built in 21 segments at strategic points along the Rio Grande, must be able to withstand a crash by a 10,000-pound (4,545-kg) vehicle traveling at 40 miles per hour (64 kph), but also be “aesthetically pleasing,” the agency said.

The wall is part of a federal plan to build 700 miles of fencing along the U.S.-Mexico border.

The border protection agency said the wall would mostly be built on river levees, but also would cross private land and encroach on state parks and the Lower Rio Grande Valley National Wildlife Refuge.

The refuge is considered one of the most biologically diverse wildlife sanctuaries in the nation and environmentalists say the fence could harm endangered species such as ocelots and jaguarundi found there.

Many local leaders in southern Texas, which is heavily Hispanic and has strong economic and cultural ties to Mexico, have criticized the border wall as unnecessary and an affront to Mexicans.