"It is a completely baffling thing and it is very frustrating," the story quoted UC Cooperative Extension forestry advisor Yana Valachovic.

The pathogen was found in waterways even after all runoff was halted, infected material was removed and the surrounding area was fumigated, the article said.

Even more mystifying, two Humboldt County streams tested positive for spores matched genetically to a nursery that is at least a mile away with no hydrological connection and no way for runoff to reach the stream.

"There is some connection that I don't understand," Valachovic was quoted. "The genetics match with the nursery, so it appears that it originated in that nursery. How it got to the stream is undetermined."

Catherine Eyre, a UC Berkeley post-doctoral researcher, said spore contamination was found in the water in at least half of the 14 sites tested this year in and around the Crystal Springs Reservoir, which supplies drinking water to millions of people in Bay Area. The spores pose no health risk to humans, but scientists are tracking it to halt its spread around the state.

"We're looking at how far the pathogen can travel and how long it can survive," Eyre was quoted.