THE SOUTHLAND DELUGE : Rescuers Can’t Reach Boy, 15, in L.A. River : Emergencies: Dozens of motorists stop to help. The search will resume today for the bicyclist who was carried nearly 10 miles by the current.

A 15-year-old boy caught in the churning Los Angeles River was swept nearly 10 miles across the San Fernando Valley--passing dozens of would-be rescuers who chased him from bridge to bridge--and disappeared less than half a mile from where firefighters waited to pluck him from the murky waters.

Dozens of passing motorists stopped to help rescue workers--some of them dangling from bridges--try to save Adam Paul Bischoff from the 35 m.p.h. current that swept him from Woodland Hills to Reseda in less than an hour.

Firefighters and police officers chased Adam along the debris-filled channel. But their efforts were frustrated by strong currents, floating debris and the boy’s inability to grab the ropes, garden hoses and inflatable rafts tossed to him.

After about 45 minutes in the chilly water, Adam, who had been waving at onlookers as he struggled to stay afloat, disappeared between Lindley Avenue and Balboa Boulevard, where rescue workers waited to grab the boy from a slow-moving stretch of the channel.

“If that kid could have held on another half-mile, I think we could have gotten to him,” Assistant Fire Chief Tony Ennis said.

Helicopters hovered over the area near the Sepulveda Basin for most of the afternoon, but the search was called off at dusk with little hope left of finding the boy alive. Rescuers speculated that Adam’s body might be tangled in the trees that grow on the river bottom and will be difficult to find until the swollen river subsides.

The drama began about 11:20 a.m., when police say Adam, a 10th-grader at El Camino Real High School, was riding with a friend along the Arroyo Calabasas near his home. The friend told investigators that the boy rode his bike into the water and it was knocked out from under him by the current.

When he tried to grab the bike, Adam was pulled into the channel and swept downstream.

Several residents along the channel heard the boy’s screams for help as he was carried along.

One man who called 911 said he heard a high-pitched voice shouting: “I fell in the wash! Please help me!”

“At first I thought it was a joke,” said the man, who lives near Shoup Avenue and asked not to be identified. “But he passed so quickly, I knew he was in trouble. I called 911.”

Emergency crews quickly stationed themselves on bridges between De Soto Avenue and Balboa Boulevard, lowering ropes across the channel. But each rescue effort failed because Adam was unable to grab rescue equipment or too weak to keep his grip. On a pedestrian bridge near Reseda High School, Detective Steve Finchen said Adam briefly grabbed a rope, but let go after about 35 seconds.

Fire Capt. Steve Bascom said such scenes were repeated over and over as Adam grew weaker and weaker and was whisked past rescue workers. “He reached for the rope, missed it and was gone,” Bascom said.

With a garden hose tied around his waist, Los Angeles Police Officer Bob Laskowski was lowered down the concrete banks of the channel and tried to use a pole to grab Adam, who passed within 15 feet of him.

“That was the last time I saw him,” Laskowski said.

In an effort to reach the boy, Laskowksi stepped into the channel and was pulled into the water. Laskowski was pulled to safety by the other officers. “I was hanging on to the hose and the other officers reeled me in like a fish,” he said.

“I can’t believe how strong the current was,” Laskowski said. By comparison, the Colorado River travels about 25 m.p.h. at its fastest points, about 10 m.p.h. less than the Los Angeles River on Wednesday.

In addition to police and firefighters, a trail of motorists followed the procession across the Valley, offering assistance and throwing ropes. “I threw a rope from the back of my truck, but he couldn’t get it,” said Carlos Marfil, 40, of West Hills. “He saw it, but he couldn’t even pick up his arm.”

The final rescue point was at Balboa Boulevard, where firefighters tied themselves to the bridge with the hope of catching the boy before he entered the Sepulveda Basin. Various pieces of rescue equipment tossed to Adam floated past, but there was no sign of the boy.

By 12:15 p.m., most of the rescue workers were dispatched to other emergencies. Only a handful remained to walk along the riverbanks as helicopters hovered overhead.

Police said they would resume the search for the youth this morning.

Times staff writers Richard Lee Colvin, Amy Pyle and Jim Herron Zamora contributed to this story.