Malakoff Diggins State Historic Park Watershed Assessment

The Sierra Fund has been working to assess and address the ongoing water quality problem from contaminated discharge from hydraulic mines since 2011. One of California’s largest and most iconic hydraulic mines, Malakoff Diggins, has served as a model project for the region. 

“The Sierra Fund’s Humbug Creek Watershed Assessment Project benefited from sample analysis at certified trace metal laboratories and state-of-the-art stream gage and monitoring equipment to quantify the annual sediment and mercury loads contributing to the Wild and Scenic South Yuba River.”

Carrie Monohan, Ph.D., Program Director


Hydraulic mining power-washed away the auriferous gravels of ancient rivers and laced the gravels with liquid elemental mercury during gold extraction practices. The mercury left behind continues to bioaccumulate and biomagnify within the food web, exposing humans and wildlife to a dangerous neurotoxin over 100 years later. The historic 2 x 1-mile hydraulic mine pit is the centerpiece of California’s Malakoff Diggins State Historic Park, and on the National Register of Historic Places. It discharges egregious levels of sediment and mercury every time it rains.


In April 2015 The Sierra Fund published the findings of the first four years of work on this project in the Humbug Creek Watershed Assessment and Management Recommendations report. This report serves as the guiding document for an alternatives analysis being conducted by California State Parks and its subcontractors to determine the best approach for site remediation.


Hydraulic mine sites release sediment and mercury and are a significant predictive variable for fish mercury concentration in downstream water bodies (Alpers et al., 2016). This project creates a model for scientific assessment of hydraulic mines and multidisciplinary collaboration that can be replicated at similar sites across California. Success will be measured by the reduced sediment and mercury loads discharged to the Wild and Scenic Yuba River.

Next Steps

The Sierra Fund continues to coordinate with State Parks and their subcontractors to inform ongoing assessment efforts based on previous findings and lessons learned. In addition, The Sierra Fund maintains the longest operating stream gage at the site, measuring turbidity and discharge every 15 minutes year round. Critical to this project is the selection of alternatives that preserve and protect the cultural resources of the site while incorporating cutting edge solutions to address the ongoing water quality problem created by the hydraulic mine pit discharge to Humbug Creek and the South Yuba River.

Project Funders and Partners

California State Parks
Sierra Nevada Conservancy
Department of Water Resources
Bella Vista Foundation
Teichert Foundation
The Joseph & Vera Long Foundation
The Rose Foundation for Communities and the Environment
California State University, Chico
South Yuba River Citizens League