While what caused last month’s yellow plume in the South Yuba River has yet to be determined, the Sierra Fund believes it has a strong case. In a report, it says hydraulic gold mine sites are notorious for sedimentation discharges after strong rains. It describes the rain that fell just before the plume was discovered as unusual for that early in the fall season. The group’s CEO, Izzy Martin, says Humbug Creek receives surface flows from one of the largest hydraulic mining sites, Malakoff Diggins…

Martin says even though there have been early fall rains over the years, the influence of climate change, with more droughts and heavy storms, is increasing the frequency of these types of discharges…

Martin says the Sierra Fund has been talking to state water investigators about the issue, including this incident. She points out that the hydraulic mining from the last century has never been completely cleaned up. She says the main concern is mercury, which can travel long distances and contaminate fish, making them unsafe for consumption.