The last time members of a Northern California Indian tribe held a coming-of-age ceremony beside a popular river, they were heckled by boaters. Drunks yelled racial taunts, jet-ski engines roared and a woman flipped down her bathing-suit top as she passed them.

The tiny group known as the Winnemem Wintu saw it as their right to hold a sacred ceremony on their ancestral land undisturbed. But some vacationers on the McCloud River arm of Lake Shasta near Redding were more in tune with a man who shouted: “Hey dude — it’s our river too!”

This weekend the Winnemem are trying again, preparing an elaborate four-day rite for two teenage girls. A third was set to participate but opted out because of anxiety about outsiders’ reaction, said Winnemem chief Caleen Sisk-Franco.

The U.S. Forest Service is putting up signs announcing a “voluntary closure” along the shore and on a 200-yard stretch of the river. Still, the Winnemem are bracing for trouble during the ceremony, called Balas Chonas.

“We know what to expect,” said Sisk-Franco. “We know there will be some hostile people who go through the voluntary closure. It’s incredible that the U.S. Forest Service can’t find any way to stop them.”

The Forest Service weighed the public’s right to recreation against the tribe’s right to its rituals and decided it had no legal authority to shut off the contested portion of river during the ceremony.

Supporters of the 125-member tribe say they will take to the water themselves, asking boaters to reverse course to avoid disrupting the rites. Forest Service employees will deliver the same message, according to Debbie Davis, of the Environmental Coalition for Water Justice, a Sacramento-based group that has taken up the tribe’s cause.

“I have to say that the Forest Service has tried very hard to figure out how to do a full closure,” she said. “The challenge is that the tribe isn’t federally recognized.”

Under a 2008 law, agencies can temporarily bar the public from areas in which tribes are conducting rituals. But those tribes must be federally recognized — and most California tribes, despite lengthy attempts to meet federal criteria, are not.

In a letter to tribal representatives, J. Sharon Heywood, supervisor of the Shasta-Trinity National Forest, said it’s the Shasta County Sheriff’s Office that has jurisdiction over boat traffic on the lake. A spokesman for the sheriff’s office referred all questions to the Forest Service, where a spokeswoman had no comment.

Lacking federal recognition has made life more difficult, say the Winnemem. Last year, they sued six federal agencies, accusing them of destroying sacred sites during road and bridge construction. “The government’s position basically is that since we’re not recognized, we’re not really Indians — and can’t have sacred sites,” Sisk-Franco said.

The Winnemem, whose ancestors lived along what is now the McCloud River, say they ceded 4,800 acres to the federal government in return for land that was never delivered.

Meanwhile, the creation of the lake flooded many of their sacred sites.

Only when the water level drops in the summer does the place they call Puberty Rock emerge. It’s a central spot in the coming-of-age ritual, in which the girls sleep several nights in a cedar-bark lodge on one side of the river. On the day after a full moon, they and their minders swim the 200 feet or so across the McCloud as tribal members on the other side welcome them to womanhood.

In 2006, the tribe performed its first such ceremony in 80 years.

On the final day, Shasta County sheriff’s deputies blockaded the river for several hours after the Forest Service asked them to step in.

steve.chawkins@latimes.com