The source of the yellowing of the South Yuba River about two weeks ago remains a mystery. Andrew Altevogt is the Assistant Executive Officer for the Central Valley Regional Water Quality Control Board. He says aerial photographs had indicated the source of the sedimentary plume was likely at a home on Kilham Road with alleged code violations…

But Altevogt says officials still believe they’ve narrowed down the geographical area, that the plume originated not far from the home. That includes Bureau of Land Management public lands. It also looks like recent wet weather was a factor…

Altevogt also says it’s not believed the plume was toxic, after chemical tests were taken. Nevada County officials say mining has historically occurred in this area, with several exposed cliffs typically associated with hydraulic mining easily visible. There was a spike of E.coli levels initially, which prompted a swimming ban for a few days. But that appears to be incidental to the plume.