The Los Angeles River can’t guarantee flowing water all the time, but the imposing concrete bed has seen an unending stream of film crews going back six decades.

In 1954, actors James Whitmore and James Arness hunted the river’s dark tunnels, checking for mutant killer ants in the B-flick “Them!” More recently, Arnold Schwarzenegger narrowly escaped a cyborg assassin in “Terminator 2: Judgment Day,” filmed in a San Fernando Valley section of the river in 1991. And in 1978’s “Grease,” John Travolta won the pink slip of a rival’s car during a famous drag race that took place in the riverbed near downtown.

The river has starred in enough feature films, television shows and commercials that like the Griffith Park Observatory or the Hollywood sign it’s become a tourist attraction in and of itself.

“It’s one of those L.A. icons that people have seen so often in movies or on television that when they come here they have to see it for themselves,” said Mike Bobenko, senior vice president of operations for the Entertainment Industry Development Corp.

Before the Great Depression, the L.A. River was a gushing stream that cut through the San Fernando Valley to downtown before turning south to empty into the Pacific Ocean near San Pedro.

But after a disastrous flood that killed more than 50 people in 1938, the Army Corps of Engineers reined in the river by digging up the muddy bed and constructing the concrete flood channel that exists today.

The $370 million project was a key part of President Franklin Roosevelt’s job-creation program for the region. It transformed Los Angeles by creating three reservoirs along a 100-mile concrete course.

The result, among other things, has been far less flooding and many more camera crews. Many shoots use areas of the river near downtown, with its arched bridges, ominous tunnels and skyline views.

Costs for a simple shoot can run as little as the $450 filing fee for a film permit, which often times can be obtained in about four hours, according to EIDC officials. But the Army Corps of Engineers, which has joint authority over the river with the city and county of Los Angeles, can take longer if it needs to determine whether filming would harm any endangered species that inhabit the river.

There can be other complications, such as the weather. During the winter, rain can cause raging currents that further delay shooting.

Then there’s the unexpected discovery: river inhabitants. Bobenko said the situation is usually handled without calling in outside authorities. “The companies usually deal with the encampments on their own,” he said. “Usually $5 or $10 a person will be encouragement enough to clear out.”