Alaska's once crystal-clear rivers now resemble dirty orange soda, puzzling researchers

• Researchers noticed that Alaskan streams had turned bright orange.
• Warmer summers and melting permafrost may be turning the water rusty and acidic.
• Scientists are racing to figure out the cause so they can predict where it could happen next.

"In a lifetime of descending rivers," John McPhee wrote of Alaska's Salmon River, "this was the clearest and the wildest river."

The writer who toured the Salmon in 1975 might not recognize it today. Its clear waters have turned orange.