Lake Oroville Update - May 8, 2026

Blue Green Algae Monitoring

California Department of Water Resources’ (DWR) environmental scientists began monitoring for blue-green algae and their toxins last week within the Oroville-Thermalito Complex. Monitoring occurs during the summer with water samples taken at various locations regularly, which are sent to a lab for toxin analysis. There are currently no harmful algal bloom (HAB) advisories for Lake Oroville, the Thermalito Forebay, or the Thermalito Afterbay. 

Blue-green algae (cyanobacteria) are a natural component of ecosystems. Under certain conditions, including warmer temperatures and increased nutrient loads, algae can grow rapidly causing “blooms.” Algal blooms sometimes produce toxins that can be harmful to people and animals. Algal blooms can make the water appear green, blue, or brown in color. Seeing colors, mats, foam, scum, or paint-like streaks in the water may indicate a bloom is present. Keep animals and children away from the water when a suspected bloom is present and report blooms immediately to the California Water Resources Control Board.

If testing reveals elevated levels of cyanobacteria toxins, DWR staff will work with California’s Regional Water Quality Control Board and recreation area managers to notify the public and post advisory signs at affected waterbodies. To learn more about HABs, or to report a HAB visit the Water Board’s website.

Feather Fiesta Days

For more than 70 years, Feather Fiesta Days has been Oroville’s premier hometown celebration. Festivities are held over two weekends - Saturday, May 2 through Saturday, May 9 with a large variety of activities. Get the party started with a Chili Cook-Off, followed by the Kiwanis Kiddies Day Parade, and Feather River Recreation & Park District's Concert in the Park. Then head to downtown Oroville on Saturday, May 9 for the Gold Rush Car Show, Feather Fiesta Days Parade, craft fair, and vendor and food booths. 

Stop by DWR’s booth in downtown Oroville between 10 a.m. and 4 p.m. on Saturday, May 9. DWR will share information about Lake Oroville recreation areas and offer a craft activity and community art project. Create Feather River-inspired tissue paper stained glass art or help decorate a tissue paper banner mural. Staff will display your beautiful banner artwork at the Lake Oroville Visitor Center for the next few weeks.

Learn more about scheduled Feather Fiesta Days activities at visitoroville.com.

Temporary Closure of Rabe Road Shooting Range

The California Department of Fish and Wildlife (CDFW) is temporarily closing the Rabe Road shooting range on Wednesday, May 13 so CAL FIRE crews can prepare the area for a prescribed burn later this month. The Rabe Road shooting range is also routinely closed for a couple of hours in the morning on the last Thursday of each month for cleaning. The range is open daily from sunrise to sunset for rifles, pistols, shotguns, and archery. There is no rangemaster on site. Only paper and clay targets are permitted.

DWR Modifies its Invasive Mussel Inspection Program at Oroville

DWR has modified its inspection program for invasive mussels at Lake Oroville, the Thermalito Forebay, and the Thermalito Afterbay. Effective April 29, watercraft inspections, decontamination services, and seal checking at the Oroville facilities are no longer required. Blue Oroville seals are no longer required to launch watercraft and owners have permission to remove seals themselves, as inspectors will no longer be stationed at launch ramps. DWR will also reopen facilities that were closed to trailered launching including those at the Thermalito Forebay and Thermalito Afterbay. At locations requiring the removal of physical barriers, additional time will be required for crews to fully reopen facilities. Launching access at Lake Oroville will once again be available 24 hours a day, every day.

The decision to implement an invasive mussel boat inspection program at DWR’s Oroville facilities in May 2025 was based on available information about how best to protect DWR infrastructure from golden mussel establishment. While DWR does not control many of the lakes and reservoirs upstream of Lake Oroville, it quickly established a program to reduce the potential risk of invasive mussel introduction through recreational boating. Additional analyses of golden mussel biology and habitat requirements, as well as an assessment of DWR’s Oroville infrastructure, have shown a lower risk of golden mussel establishment than was originally anticipated.

During the last year, DWR performed a vulnerability review of Lake Oroville, the Upper Feather River Lakes, the Feather River Fish Hatchery, and Oroville-Thermalito Complex infrastructure to golden mussel colonization. The seasonal water temperature conditions at Lake Oroville and the Upper Feather River Lakes were evaluated based on a 2017 study in which researchers assessed the conditions golden mussels need to survive and reproduce.

For golden mussel maturation and reproduction to occur, water temperatures greater than 61.7°F for about 150 days are necessary for successful spawning and the formation of veligers, the larval stage of mussels. For veligers to complete their development and settle into a hard-shell mussel, water temperatures must be nearly 70°F for approximately 70 days.

Temperature thresholds for golden mussel maturation exist within the top 60 feet of Lake Oroville, meaning that sustained mussel populations would be confined to specific areas of the reservoir, such as floating infrastructure, and boats that remain on the water for lengthy periods. Mussels could survive in shallow shoreline locations until lake levels drop, at which point they would dry out and die. Extended cold water temperatures in the Upper Feather River lakes, the depth of Lake Oroville, and the continuous cold water releases from Oroville Dam to support salmon habitat are limiting factors for golden mussel spawning and larval development. Any veligers that are transported through the dam at lower lake elevation temperatures would be unlikely to survive, would have a difficult time growing, and would not have a significant impact on the Feather River Fish Hatchery and Oroville-Thermalito Complex powerplants.

Given this analysis of potential impacts to State Water Project infrastructure, DWR is no longer requiring watercraft inspections at Oroville. Ongoing water testing and visual inspections of infrastructure for invasive mussels will continue. Golden mussels have not been detected at DWR’s Oroville f[BA1] acilities or the Upper Feather River lakes. Program changes are being coordinated with local recreation partners at the California Department of Parks and Recreation and CDFW.

DWR continues to partner with federal, State, and local agencies to mitigate golden mussel colonization throughout California’s water systems. This includes coordinating with partners on a statewide reporting system for watercraft, continuing public education campaigns about golden mussels and how they spread, ongoing studies about effective treatment options, and implementing a variety of mitigation and maintenance actions to maintain State Water Project operations that are currently affected by the presence of golden mussels.  

When recreating on California’s waterways, always remember to:

• Clean aquatic plants and animal material from your boat, trailer, and equipment before leaving the ramp or parking lot.
• Drain ballast, bilge, livewells, and other water-containing devices, and never drain back into the waterway.
• Dry equipment, including bilge, ballast tanks, and livewells, before launching into another body of water.

More details about DWR’s invasive mussel inspection program are available at water.ca.gov/mussels.

Feather River Fish Monitoring Station

DWR resumed operations of the Feather River fish monitoring station on March 4, 2026 to capture the return of spring-run Chinook salmon. Monitoring was temporarily suspended at the end of December 2025 due to anticipated high flows in the Feather River. Upstream migrating fish totals between March 4 and May 4, 2026 are:  

• Spring-run Chinook salmon: 3,472
• Steelhead: -21 (most likely kelts moving downstream)
• To see previous year data, visit CalFish.org.

Current Lake Operations

Lake Oroville is at 896 feet elevation and storage is approximately 3.36 million acre-feet (MAF), which is 98 percent of its total capacity and 122 percent of the historical average.

Feather River flows are at 650 cubic feet per second (cfs) through the City of Oroville with releases from the Thermalito Afterbay River Outlet at 400 cfs for a total Feather River release of 1,050 cfs downstream. DWR continues to assess Feather River releases daily.

The public can track precipitation, snow, reservoir levels, and more at the California Data Exchange Center. The Lake Oroville gage station is identified as “ORO.”

All data as of 11:59 p.m. on 5/7/2026.