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Water temperatures in Wyoming trout fisheries have already increased 2 degrees, a trend that could reduce fishing opportunities in the state by 50 percent by the end of the century, a report by conservation groups says.

Wyoming rivers such as the Firehole, the North Platt and the Upper Green are considered most at risk in the state, according to the Natural Resources Defense Council and Trout Unlimited.

Scott Yates, a Wyoming spokesman for Trout Unlimited, said scientists anticipate a 2- to 5-degree increase in Western water temperatures in the next century.

The warmer water could have serious consequences for the state’s roughly $400 million fishing industry. In Wyoming and Idaho, the Snake River and tributaries such as the Henry’s Fork generate about 1,400 jobs and $46 million annually, according to 2002 data.

“[The study] paints kind of a dismal picture,” Yates said. “It’s pretty stark in terms of the loss of overall habitat.”

Yates said trout thrive in water that ranges from 50 degrees to 64 degrees Fahrenheit. Last summer, temperatures in the Firehole River in Yellowstone National Park reached about 82 degrees, prompting a die-off that claimed thousands of rainbow and brown trout. The Firehole River is partially warmed by the park’s thermal features, which made the river more susceptible to heat-induced die-offs.

According to the report, water temperatures in Wyoming have already increased by 2 percent, comparing a five-year average recorded from 2003 to 2007 with average water temperature throughout the 20th century.

Another 1.5-degree increase in temperature could reduce fisheries by 7 percent to 16 percent, and a 4.8-degree increase could reduce fisheries by 42 percent to 52 percent, the report says.

Despite the dire news, Yates said, opportunities exist to help prevent the habitat loss. On a planetary scale, industrialized nations need to reduce emissions of greenhouse gases such as carbon dioxide and methane by 2050, he said.

Locally, Yates said, researchers, fisheries managers and conservation groups can work with landowners to ease the effects irrigation has on Wyoming’s waterways.

“There are a lot of ways we work with ranchers to address their operational needs while allowing fish to find better habitat,” he said. “I think there are ways to partner with ranchers on steam-flow restoration, as well. We’re going to have to sit down with multiple stakeholders.”