JACKSON (AP) -- Fishing in Wyoming could decline sharply over the rest of the current century because of increasingly warm water, a report by conservation groups warns.

Trout Unlimited and the Natural Resources Defense Council say fishing opportunities in the state could drop by 50 percent by the end of the century if water temperatures continue to rise. The groups say Wyoming rivers such as the Firehole, the North Platte and the Upper Green are most at risk.

Scott Yates, a Wyoming spokesman for Trout Unlimited, said scientists anticipate an increase in water temperatures in the West of from 2- to 5-degrees in the next century.

The groups say warmer water could have serious consequences for Wyoming's roughly $400 million annual fishing industry. The groups say that 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."

Trout thrive in water that ranges from 50 degrees to 64 degrees Fahrenheit, Yates said. Last summer, temperatures in the Firehole River in Yellowstone National Park reached about 82 degrees, killing thousands of trout. Thermal features in the park warm the river.

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

The report states that another 1.5-degree increase could reduce fisheries by 7 percent to 16 percent. And it states that a 4.8-degree increase in temperature could reduce fisheries by more than 50 percent.

Yates said the situation demands that industrialized nations reduce emissions of greenhouse gases such as carbon dioxide and methane. Locally, he 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," Yates 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."