In November 2018, the Camp Fire started near the town of Pulga, California north of Lake Oroville. The fire burned much of the Feather River’s North Fork, the West Branch of the North Fork directly upstream of the lake, and in areas around the northern portion of the lake, as well as causing heavy damage to the towns of Concow and Paradise, in Butte County.

Because of the proximity to Lake Oroville, a State Water Project facility, there were concerns that runoff from the burned area could negatively affect the water flowing into the lake. To investigate this potential impact, the California Department of Water Resources (DWR) conducted a comparative study upstream, within, and downstream of the burned areas to assess water quality impacts to the lake. This study began soon after the fire was contained and continued through the spring of 2020.

Monitoring efforts during this study included the collection of water quality samples and measurements timed to occur shortly after moderate to large rainfall events following the fire. An additional non-rainfall related sample in the summer was also collected as a comparison. Measurements of water quality parameters in the field included specific conductivity, pH, water temperature, dissolved oxygen, and turbidity. Water quality sample collections were sent to the laboratory for analysis of common analytes including metals, nutrients, minerals, anions, solids, and organic carbon. Additionally, several samping events included collections and analysis of polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB).

During the study, sample collections occurred at locations on the North Fork Feather River upstream of Lake Oroville at sites upstream and downstream of the fire-affected watershed. Additionally, samples were collected on the lake at sites close to the inflows of the North Fork Feather River and West Branch of the North Fork Feather River. But, because of issues with sample representativeness, these sites were not sampled in the second year of the study. Lastly, the study examines the results of water quality samples that were and have been collected near the Lake Oroville Dam as part of DWR's long-term lake monitoring program.

Results from the first year’s samples upstream of the lake showed significant increases in several analytes in the first samples collected, suggesting the early rainfall events had a flushing effect on the watershed. Later and larger storms showed smaller increases, likely because of dilution effects in the rivers. Likewise, samples in the second year confirmed the flushing effects from early storms and showed increases in analyte concentrations similar to the first year’s samples. Analytes that showed large increases were typically those associated with or bound to sediment particles including certain undissolved metals, minerals, nutrients, suspended solids, and turbidity. Conversely, several analytes and groups of analytes showed no change or were not detected downstream of the burned area including most dissolved metals, chloride, mercury, PAHs, and PCBs.

Lastly, results from samples collected at the Lake Oroville dam site showed higher concentrations for many of the same analytes that increased in the samples upstream of the lake. This indicated some degree of influence from the burned area runoff on concentrations in the lake or from previously unidentified natural seasonal variation. The determination of the degree to which either of these influences affected concentrations in the lake as a whole was beyond the scope of this study. Nevertheless, analytes that had increased during the winter and spring all returned to normal concentrations by summer, and no analytes showed a persistent increase in the lake following the fire.

Detailed information about the study design, sample timing, rainfall totals, river flows, and the detailed water quality analysis and findings can be found in the technical memorandum written for this study. The laboratory results and field measurements for all sampling associated with this study can be found in the Compiled Study Analytical Results file. The laboratory results and field measurements for 2018-2020 collected as part of the long-term Lake Oroville monitoring program can be found in the Compiled Dam Site Analytical Results file.