A warming planet could have dire results for those who enjoy freshwater fishing, according to a National Wildlife Federation report that was released on Wednesday, and a leading Maine outdoor advocate worries that climate change may eventually cost the state its iconic brook trout population.

Changes in habitat and ecosystems and severe weather events are among the threats, which the report predicted could cost states billions over the coming century.

“The loss of recreational fishing opportunities could have real economic impacts across the nation, particularly in rural areas that depend on angling-related expenditures,” the report stated, estimating that 26 million adult anglers spend a total of $26 billion on fishing, nationwide, today.

According to the report, an “estimated 55 percent of the nation’s river and stream miles do not support healthy aquatic life largely due to nutrient pollution, sedimentation and habitat degradation.” One concern that the report addressed is severe weather that accompanies climate change will lead to more polluted runoff making its way into rivers, streams and lakes.

During a teleconference hosted by the Natural Resources Council of Maine, Dylan Voorhees, clean energy director for the Natural Resources Council of Maine, said the report was an important warning that outdoors enthusiasts should pay close attention to.

“The bottom line of this report is, climate change is the most serious threat to America’s freshwater fish,” Voorhees said. “Climate change is already having disturbing effects.”

George Smith, the former executive director of the Sportsman’s Alliance of Maine, said the report worries him.

“I was born and raised a brook trout fisherman,” Smith said. “I think the biggest challenge and maybe the thing that might wipe out brook trout despite our efforts is climate change.”

Wildlife biologist Eric Orff of the NWF said weather patterns have changed in recent years.

“Over the last 25 years I didn’t witness the [climate] changes that I’ve seen in the last five,” Orff said.

At his home in Epsom, N.H., Orff said he can see the Suncook River. And in recent years, that river has been raging more often than he can remember.

“The past five years, we’ve had three 100-year floods,” Orff said.

According to the report, in 2011 Maine had 283,000 freshwater anglers who spent more than $252 million in fishing-related expenditures. In other states, angling is far more important economically. Tops on the list: Minnesota, where 1.4 million anglers spent $2.3 billion in 2011.

Maine was cited specifically in the report as a state where climate conditions have led to problems.

At Lake Auburn, a subsequent six-inch rainfall over a 24-hour period led to erosion around the lake; the nutrients that were flushed into the lake is thought to have helped lead to excessive algae blooms, and recorded dissolved oxygen levels in the deeper areas of the lake reached all-time lows. Many of the lake trout in Lake Auburn died as a result.

In northern states such as Maine, ice fishing’s future could also be a concern, researchers said. With hotter summers and warmer winters, there are fewer cold days during which a suitably thick ice cover can form. Winter temperatures in the northeast and midwest have increased from 3 to 4 degrees Fahrenheit since 1970.

Jason McKenzie, whose family has owned Suds N’ Soda Sports in Greenland, N.H., for decades, said when winter doesn’t arrive in the Seacoast region of the state, his business takes a beating.

Suds N’ Soda is a true one-stop shop, selling everything from groceries, sandwiches and beer to guns, ice fishing gear and bait.

“When you don’t have a winter, you’re twiddling your thumbs,” McKenzie said. “How much business have we lost in a bad winter? All of it. Or two-thirds of it, anyway.”

Potential monetary loss isn’t the only thing at stake, researchers pointed out. Anglers in Michigan are concerned that an ice-fishing heritage is being lost.

Smith, Orff and Voorhees agreed that actions that improve fish habitat — replacing culverts that block fish passage, for instance — was an essential step in delaying the effect of climate change as long as possible. But Voorhees said focusing on what he says is the cause of climate change was key.

“We continue to pour carbon into the atmosphere,” Voorhees said. “I would suggest that the single largest thing we can do nationally to reduce global warming pollution would be to implement standards for power plants, and the Environmental Protection Agency has proposed a set of global warming standards for new power plants that need to be finalized.”

Establishing standards for power plants that already exist is the next step, he said.