Every time it rains, workers in Long Beach rush to the mouth of the Los Angeles River to scoop up the floating islands of plastic bottles, grocery bags and other debris before it’s all swept onto local beaches or pulled out to sea.

Now, a deceptively simple solution is underway to fight the ongoing problem of river trash by intercepting it before it’s washed into the river in the first place.

Over the next year, 16 cities in southeastern Los Angeles County are installing screens beneath nearly every storm drain that flows into the lower Los Angeles River.

Once the custom-built stainless steel devices are installed inside nearly 12,000 catch basins, authorities expect them to keep 840,000 pounds of debris — the equivalent of about 450 Volkswagen Beetles — from reaching the ocean each year. The garbage that washes off city streets and highways has long been identified as a major source of pollution that can degrade coastal habitat and float thousands of miles away on ocean currents.

The project will also help communities along the Los Angeles River comply with state and federal clean-water rules that require they capture nearly all the trash that for years has washed into the river.

“This stuff is not just going into the ocean and disappearing,” said Jonathan Bishop, chief deputy director of the State Water Resources Control Board. “The long-lasting parts of it, which are primarily the plastics, are essentially moving their way through the currents, impacting marine life and impacting our beaches and our local waters too.”

Described as the largest debris-capturing project in the nation, the clean-up effort is being undertaken by the Gateway Authority, a coalition of cities and public water agencies in southeastern L.A. County, using $10 million in federal stimulus dollars.

The project could serve as a model for similar plans to use grates to cut down on the garbage released in the San Francisco Bay Area. Public works officials have also proposed the same protections in other urban waterways in the Southland, including the San Gabriel River and Ballona Creek.

Crews have gradually been installing a few thousand similar devices in unincorporated Los Angeles County, but this latest project marks the largest and most aggressive attack on river trash.

Officials hope the screens will not only stem the flow of trash onto local beaches and harbors, but also prevent the junk from being carried to the distant reaches of the Pacific Ocean, where scientists have documented a massive vortex of marine litter known as the Great Pacific Garbage Patch. Some researchers say the high concentration of floating plastic debris spreads over an area larger than Texas.

Of greatest concern to environmentalists is discarded plastic packaging such as food wrappers, bottle caps and straws, which easily float through unprotected storm drains and toward the coast.

A soda bottle tossed to the curb in Downey, for instance, is destined for the storm-water system, which will shuttle it to the Los Angeles River and eventually to the ocean about 15 miles away.

The screens to be installed in southeast L.A. County represent a simple, even low-tech, concept, serving as strainers just below the drains where water from city streets flows into the storm-water system. The 5-millimeter mesh will catch debris as small as a cigarette butt. Workers will have to periodically open a manhole and suck out the trash with a vacuum truck.

Several thousand storm drains in the most littered areas of the county will also be outfitted with street-level retractable screens that act as a second-level of defense, keeping most trash above ground level.

Long Beach, where nearly a third of the devices are being installed, stands to benefit the most because it is at the receiving end for trash flowing from dozens of communities upstream.

“You’ve seen the little signs that say ‘Drains to Ocean’?” said Long Beach City Engineer Mark Christoffels. “Look, that hamburger wrapper that you just tossed in the gutter, it goes through and eventually ends up at our beaches and in the ocean. Now, we’re making a statement here, that we’ve got to capture as much of this as we can.”

But don’t expect the immediate elimination of all trash along the coast, experts said.

The grates, of course, do nothing to reduce littering at the beach or wind-blown debris, and the smallest fragments of plastic and foam will flow through the screens. To avoid flooding, the devices are also designed to swing open during heavy rains.

“It’s certainly not a permanent solution in the sense of eliminating the plastic discharge to the ocean,” said Charles Moore, founder of the Algalita Marine Research Foundation, who has studied the flow of garbage through the Los Angeles and San Gabriel rivers and trawled for trash thousands of miles away on expeditions to the North Pacific.

Moore said much of the debris making it to the ocean is less than 5 millimeters across, mostly industrial plastic and foam pellets that won’t be caught by the screens.

Gateway Authority officials say making the grates any finer would make it difficult for water to flow through them. If the project is successful, they hope communities farther upstream will follow their lead and install the same equipment.

At as much as $4,000 per catch basin, however, the sheer expense is likely to deter many cash-strapped local governments.

Moore of the Algalita Foundation said plastics manufacturers ought to shoulder some of the cost of keeping their products out of the ocean.

“You can’t put this external cost to the throwaway society onto the municipalities and taxpayers,” he said. “They’re asked to do all that work, when really, the plastic industry itself needs to be held responsible.”

tony.barboza@latimes.com