Two years ago, near the end of California's devastating drought, Tom Moore stood on the banks of the depleted Kern River in Southern California and looked out at the slow-moving waters dejectedly.

"We call that a creek," he said of the mighty Kern.

Moore is the owner of Sierra South, a whitewater recreation company in Kernville, Calif. And with the drought, there wasn't much in the way of whitewater.

Oh, how things change.

A wet winter and near-record snowpack has left the Sierra Nevada buried in a deep, lingering snow; ski resorts in Northern California are still open. But as temperatures have risen, melting some of that snow, so too have the state's waterways.

"This is not a creek," Moore says, looking out at the Kern River on a recent hot, summer day. "This is a raging river."

The change in the water's behavior has been good for Moore and whitewater sports enthusiasts — professional kayakers are flocking to the Kern. But it's also proved dangerous. At least six people have died on the Kern River already this year. Some were playing on the water; others were just trying to cool off. Emergency workers worry there will be more.

"This is not the same river [people] may have visited last year," says Sgt. Zack Bittle, with Kern County Search and Rescue.

The water is 10 times stronger than it was a year ago, Bittle says. Riverbanks are less stable. Vegetation and brush that had grown on low shorelines during the drought are now submerged, creating invisible, underwater hazards.

"I can't recommend going in the river this year. It's just insane," Bittle says. He added that if you must go in the water, to be sure to take an expert guide.

The power of the Kern River is partly due to geography. The Kern River draws its waters from the base of Mount Whitney, the highest point in the continental U.S., more than 2 miles above sea level. From there, the snowmelt races down narrow canyons and chutes, past Kernville, to the flat, flax-colored floor of the Central Valley below.

The drop in elevation and surrounding geology gives the Kern River oomph.

But the issues with snowmelt aren't unique to Kern this year. Up and down the Sierra Nevada, waterways are flooding with snowmelt. Further up California's Central Valley, homeowners were evacuated when the King River breached the riverbank. Reservoirs are near full.

Compounding matters is the fact that water officials aren't entirely sure how much snow there is left to melt.

"What we noticed during the heat wave is that the area of snow that is still covered up there didn't really reduce from one extent to the other," says David Rizzardo, of California's Department of Water Resources. "There was just an incredible amount of depth. There's still probably easily 5, 10 feet of snow in some of these places."

Water officials don't really have any historical perspective to look at for guidance either, Rizzardo says.

Two years ago, California's snowpack was 5 percent of normal. It was the lowest ever recorded. This year, the state had one of the biggest snowpacks ever recorded — larger than the last four years combined. The jump from one to the other has made it really difficult to forecast what rivers and the landscape is going to do. The concern water officials have is that this could become the new normal.

"One of the worries with climate change is that we see extremes more often," Rizzardo says. "And the extremes are even more extreme than we've seen in the past."

Whitewater recreation companies like Moore's firm are well aware of the unpredictability. They're booking rafting trips and padding their wallets for possible thin years ahead.

Some customers have been scared off by the recent deaths and the river's strength.

Olivia Vantol is not one of them. The San Diego native is smiling as she hops off a raft and wades up to the shadowed banks of the Kern River on a recent day. She and her family just went over a Class III rapid on the river and the thrill of it is still in her eyes.

"That was my first time river rafting," she says. "I chose a great year to start apparently."

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