Watershed After Fire: New Report Summarizes Years of Water Quality Monitoring in the Sacramento Watershed

Water flowing from the forests and mountain streams of the Southern Cascades and Northern Sierra Nevada connects to communities and ecosystems throughout the watershed. Along the way, natural conditions and human activities can affect water quality. Wildfires can intensify those impacts, particularly when rain washes ash, sediment, and other materials from burn scars into nearby waterways.

DWR's Northern Region Office and the Central Valley Regional Water Quality Control Board work together through the Sacramento Watershed Coordinated Monitoring Program (SWCMP) to better understand those changes.

Building on nearly 20 years of collaborative monitoring, the latest findings offer a comprehensive look at current conditions across the Sacramento River watershed. The newly published SWCMP Final Report draws on data collected at 56 monitoring stations, where scientists tracked water chemistry, temperature, bacteria, and other indicators of water quality.

Understanding Wildfire Impacts

One focus of the final report is a case study examining water quality in areas affected by the Park Fire, which burned nearly 430,000 acres north of Chico in 2024. Researchers looked at several indicators that can show how wildfire and subsequent runoff affect a watershed, including the amount of sediment suspended in the water and levels of aluminum, iron and phosphorus, which can be carried downstream with eroded soil and ash.

Of the three watersheds studied, Big Chico Creek showed the clearest signs of wildfire-related impacts. Mill Creek showed a more moderate response associated with increased sediment, while conditions in Deer Creek were comparatively stable.

The study provides an opportunity to examine water-quality conditions in fire-affected areas and establish information that can help assess potential changes in the watershed over time. These findings contribute to a broader understanding of how wildfire-affected landscapes may influence downstream water quality and water resource management.

When vegetation is removed and soil is exposed, rainfall can easily move more ash, sediment, and debris from burned areas into streams and rivers. Wildfires can alter watershed conditions by increasing erosion and sediment runoff, which can reduce clarity and transport nutrients, metals, and other contaminants into waterways. Post-wildfire monitoring has also documented changes in dissolved oxygen, pH, and conductivity. These changes can affect aquatic ecosystems, drinking water supplies, fish habitat, and recreation.

The effects can extend well beyond a burn scar. Materials that flow downstream can influence water quality in rivers, reservoirs, and other connected waterways. For communities and water managers downstream, understanding what is entering the watershed and how conditions change as water moves downstream is important for efficient water management.

The program's approach helps provide that perspective by collecting information at multiple locations along the watershed. The Central Valley Regional Water Quality Control Board has identified long-term coordinated trend monitoring in the Sacramento River watershed as an important collaborative effort with DWR.

Building a Long-Term Record

Established in 2008, the SWCMP concluded in summer 2026 after providing a long-term record of water quality conditions throughout the Sacramento River watershed - which continues to be monitored by DWR. Although the program has ended, its 18 years of data remains a valuable resource.

That long-term record will help scientists and water managers identify changes, understand potential impacts, and support water management across the Sacramento River watershed.

The value of the SWCMP extends beyond individual fires. Its monitoring results establish baseline chemical, field-measured, bacteriological, and continuous temperature information that can be compared with past and future conditions. The program also contributed data to the State Water Resources Control Board's Surface Water Ambient Monitoring Program (SWAMP), which provides high-quality information used to evaluate the condition of California's surface waters and support water resource management.

Together, these data resources highlight the importance of water quality monitoring, a crucial metric that supports the safety of California's rivers, reservoirs, and downstream communities.

SWCMP data can be found through DWR's Water Data Library and the California Natural Resources Agency's Open Data Portal.