On a sunny stretch of the Bear River near Colfax, the cool water carries a nasty surprise for swimmers and fishermen.
Biologist Kevin Davis inspects a branch covered by algae called "didymo" that has infested the Bear River. Experts can't explain the explosive growth of the formerly little-known native California plant in the river.
The Didymosphenia geminata algae infesting the Bear River grows long stalks that can persist months after the "nuisance bloom" dies.