Lake Oroville Update - September 5, 2025

Feather River Floating Classrooms
The Department of Water Resources' (DWR) free Feather River Floating Classroom raft tours are returning this fall! Sponsored and developed by DWR, the Floating Classroom program takes participants through Feather River spawning habitat while DWR and Pacific States Marine Fisheries Commission scientists provide information on Chinook salmon conservation efforts, ongoing and planned research, restoration and monitoring projects, and fisheries management activities supported by the State Water Project.

Free rafting tours this fall are scheduled each Saturday starting October 4 through November 8. Each Saturday will have two floating classroom sessions with limited seats. Tickets are available on a first-come, first-served basis with up to four free tickets available per unique registration. Reserve your FREE floating classroom ticket on Eventbrite.

Suspected Golden Mussels Found During Boat Inspection

Inspectors for DWR's invasive mussel prevention program at Oroville found suspected golden mussels during a routine inspection of a pontoon boat Thursday afternoon. The pontoon was previously moored at the Pittsburgh Marina and had been power washed prior to traveling to Oroville. Thanks to DWR's mussel inspection program, the boat was prevented from launching at DWR's Oroville facilities.

Staff immediately contacted the California Department of Fish and Wildlife (CDFW) for further inspection and decontamination at another facility. The vessel was quarantined and will not be allowed to launch at a DWR reservoir until CDFW confirms that it is free of mussels.

DWR launched its mandatory invasive mussel inspection program for the Oroville facilities - Lake Oroville, Thermalito Forebay, and Thermalito Afterbay - in May 2025. Inspection and vessel decontamination services remain free.

Golden mussels were first discovered in the Port of Stockton in October 2024. That same month, golden mussels were discovered at the SWP's O'Neill Forebay in Merced County.

Adult golden mussels range from ½ inch to 2 inches in size and have a light to dark yellowish-brown to brown-colored shell. When golden mussel populations are established, they are difficult to control due to their rapid growth and are easily spread to new waterbodies. Golden mussels can alter aquatic ecosystems by filter-feeding on planktonic algae and changing the habitat structure, which can damage fisheries, impact water delivery systems by clogging small-diameter pipelines, screens, and filters, and impact recreation by fouling boat hulls and motors and clogging intakes and cooling lines. Mussel larvae, also referred to as veligers, are microscopic and free floating in infested waters, and can be transported in a boat's live well, ballast tank, or in the bilge if these areas are not completely drained.

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

Algal Bloom Observed in North Fork

DWR is notifying members of the public of an algal bloom in the upper reaches of Lake Oroville in the North Fork arm between Stony Creek and the train tunnel below French Creek. Initial water testing did not detect toxins, and additional samples were sent for more in-depth laboratory testing. DWR will continue to monitor the bloom and collect additional samples if conditions warrant. There is no sure way to tell if an algal bloom is toxic just by looking at it, but there are indicators that a bloom may be present.

What are signs of algal blooms?

• Small blue-green, green, white, or brown particles in the water
• Streaks in the water that look like spilled paint
• Mats, scum, or foam at the surface or along the shoreline
• Can have an odor described as gasoline, septic, or fishy

Blue-green algae (cyanobacteria) is 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.

DWR's environmental scientists routinely monitor for blue-green algae and their toxins within the Oroville-Thermalito Complex. Monitoring occurs during the summer months with water samples taken at various locations regularly, which are sent to a lab for toxin analysis. If elevated levels of cyanobacteria toxins are found while testing, 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.

Paving Work to Temporarily Close Recreation Areas

DWR continues work on a $1.9 million paving and sealing project to rehabilitate seven locations owned and maintained by the department that are heavily used by maintenance staff and public members. Project work began Aug. 18 and will continue through November 2025. Vintage Paving Company, Inc. of Winters, Calif. is the contractor for the project.

Upcoming paving and sealing work will require closures to the following public areas:

• August 18 - September 30: Afterbay Dam Crest Road/Brad Freeman Trail south of State Route 162 to the East Hamilton Road Trail Access
• September 11-12: Feather River Fish Hatchery - including the hatchery facility, upper and lower public parking lots, and river access road under the green bridge

Additional locations for future paving, sealing, and guardrail work include:

• Thermalito Powerplant Access Roads
• Thermalito Diversion Dam Powerplant
• Thermalito Power Canal Access Road

• Oroville Field Division Operations and Maintenance Center at Glen Drive
• Canyon Drive from the intersection of Oroville Dam Blvd. E./Royal Oaks Drive heading north to the dam and upper overlook
• Oroville Dam Boulevard East near Oro Powerhouse Road

DWR will provide more details about scheduled work and potential public access impacts in future newsletters. Work schedules are subject to change based on weather and the availability of equipment and materials.

Golden Mussel Inspection Program

NOTE: DWR may temporarily suspend seal checking, inspection, and decontamination services during severe weather conditions or lightning for the safety of employees.

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

Watercraft Inspection Location/Decontamination Services

North Thermalito Forebay at Garden Drive and HWY 70 in Oroville

Hours of operation: Daily from 8:30 a.m. to 5:30 p.m.

Sealed Vessel Launching

Lake Oroville

Ramp hours: Daily from 7:30 a.m. to 9 p.m.

• Spillway
• Bidwell Canyon

Extended Ramp hours: Daily from 5 a.m. to 9 p.m.

• Lime Saddle
• Loafer Creek

Thermalito Afterbay

Ramp hours: Daily from 1.5 hours before sunrise to 1 hour after sunset

• Monument Hill

Thermalito Forebay

Ramp Hours: Daily from 8 a.m. to sunset

• North Forebay (Non-motorized vessels only)

Feather River Fish Monitoring Station

Between Jan. 30 and April 20, high flows in the Feather River required the temporary removal of fish monitoring equipment resulting in lower spring-run estimates. Upstream migrating fish totals through the Feather River Fish Monitoring Station between Jan. 1 and Sept. 2, 2025 are:

• Spring-run Chinook salmon (April 16 through June 30): 17,743
• Fall-run Chinook salmon (July 1 through present): 741
• Steelhead: 208
• To see previous year data, visit CalFish.org.

Current Lake Operations

Lake Oroville is at 816 feet elevation and storage is approximately 2.28 million acre-feet (MAF), which is 67 percent of its total capacity and 112 percent of the historical average.

Feather River flows are at 650 cubic feet per second (cfs) through the City of Oroville with 5,350 cfs being released from the Thermalito Afterbay River Outlet (Outlet) for a total Feather River release of 6,000 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 9/4/2025.