LOS ANGELES — As they stood on the bank, the small and eager group exchanged the requisite disparaging jokes about the Los Angeles River, best known for its uninviting concrete channels that make many think of a drainage ditch.

"You think we’ll turn into a Teenage Mutant Ninja Turtle if the water touches us?" asked Aaron Goldstein, one of the group.

They could be forgiven for their dark humor. After all, there had not been an approved float trip down the river in more than seven decades. For many people, the river is best known from its many movie appearances, including a fiery chase in "Terminator 2: Judgment Day" and the climactic battle against giant mutant ants in "Them."

But in a few minutes, the 10 people gathered in Balboa Park, about 20 miles northwest of downtown, would take to the river in kayaks and canoes, as part of a pilot project to allow paddling on the waterway. For advocates who have spent decades fighting politicians who suggested that the river be paved over for a new freeway, the inaugural boat rides are the best sign yet that a revitalization is coming — at least on the sections lined with willow trees and cattails.

"Every great city has a river," said Steve Reizes, 50, a property manager who occasionally bikes along part of the river to commute from his home in Sherman Oaks to his office downtown. "They market riverfront properties and restaurants and all kinds of things. Why shouldn’t we have that, too?"

The 280 spots for the trips sold out within 10 minutes this month. Reizes used two computers to ensure that he could get a pair of the $50 tickets, a strategy usually associated with diehard fans looking for seat at a hot concert.

Just a few years ago, the Army Corps of Engineers decreed that the river was not even a river, with parts of it too dry to be considered much of a waterway. But last year, it reversed that decision and said that the 51-mile river could be navigated like any other, although parts of it can dry to a tiny trickle at times. This summer, the corps granted a limited permit to the Los Angeles Conservation Corps that would allow a set number of paddlers on a 1.5 mile stretch for eight weekends.

So with the sun blazing one recent Sunday morning, George Wolfe, the founder of L.A. River Expeditions and the leader of the trips, gathered the group for a brief safety lesson. Wolfe, who traveled the length of the river on an unauthorized three-day trip several years ago, gave his proverbial warning: You never travel the same river twice. Just last week, he spotted an oil barrel in the water.

"If you fall in the water, don’t panic," Wolfe said, as a few in the group laughed nervously. For many of them, it would be their first time setting foot in a kayak. "The first thing you should do is stand up. Chances are it’s just a few inches."

Perhaps aware of other fears, he added: "Also don’t worry — this water isn’t safe to drink, but it is safe for contact."

Moments later, the group headed into the water underneath a street overpass. The water was murky with grit, but the leaders encouraged the paddlers to revel in the silence and allow themselves to be immersed in nature. Within moments, plastic foam cups and beer bottles could be spotted in the water, but so could shimmering blue dragon flies and electric green duckweed algae.

Most of those on the water had seen stretches of the river before, using the bike path and walkways that line it in some parts of the city, visiting a bird preservation area. And as one participant confided, the concrete banks served as good hideouts for smoking marijuana when he was a teenager.

The view from the water seemed wholly different somehow. The 2 1/2-hour trip had plenty of stretches that felt worlds away from the city. When the group spotted a great blue heron on a branch, a reverent silence fell. The paddling stopped for a few moments as they watched the bird open its wings and glide through the sycamores.

The cameras came out again moments later when a few egrets were kind enough to stay still, stretching their long graceful necks like Hollywood starlets. (Wolfe said the birds had seemingly already become accustomed to people visiting their normally isolated habitat.)

And while it was far easier to spot plastic bags and rusting shopping carts than fish, a few people waved from the banks, where they were reeling in catfish that they said they would eat for dinner that night.

As the boaters glided through the final stretch of calm water, it was hard for them to square this bucolic scene with the concrete vistas elsewhere on the river that they knew so well.

"Why didn’t they ruin this part?" one participant wondered aloud.

The sentiment was exactly what Wolfe and other advocates wanted to hear.

"We’re at a tipping point — once they let people on, nobody will want to come off," he said. "If this is the will of the people, politicians will have a hard time arguing that this isn’t an attraction."

As the group pulled the boats ashore near the Sepulveda Dam, the afternoon sun inspired a round of celebratory beers. But on the van ride back to the starting point, Lavanya Mahendran lamented the absence of a waterfront bar.

"Instead, we’re all going to go our own ways," she said. "And just have to hope we can come back to a river again."