DURANGO — Animas River water levels sank to less than a third of average for a second consecutive low-flow year, revealing sharp rocks, which complicate a plunge through whitewater rapids.

It is one of many rivers in mountainous western Colorado where paltry H2O flows — as snow shrinks and melts away earlier, linked to climate warming — are raising concerns about the long-term viability of commercial rafting. Rafting has become a recreation industry juggernaut bringing $70 million a year of direct expenditures and an estimated $180 million of broader economic impact.

Big water traditionally boosts rafting fortunes. Federal measurements this week showed flows lagging at less than half of average on Clear Creek, the Eagle River, the Colorado River, the Roaring Fork River, and the San Miguel River — water volumes in many cases less than 500 cubic feet per second — far less than historic high flows topping 5,000 cfs.

But tourists still flocked to the Animas in Durango (455 cfs Tuesday), filling up four buses recently in the Albertson’s grocery parking lot, where Mountain Waters Rafting manager Heather Burke had just herded stragglers aboard with puffy safety flotation vests.

Her company and others endure by relying on crews adept at steering rubber rafts through rocks and maximizing splashes wherever possible. While a few riders have grumbled about low water, most still rave about their rides, Burke said. Along a heavily-trafficked stretch of the Animas south of Durango dubbed “The Smelter,” customers shrieked and smiled as currents carried them forth.

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