Lake Oroville Update - August 29, 2025

Tracking Fish Migration with the Feather River Fish Monitoring Station

Since abundant running water first began flowing through the Sierra Nevada foothills to form the Feather River, fish species like Chinook salmon and steelhead have been migrating up from the Pacific Ocean to spawn. Listed as threatened under the Endangered Species Act, monitoring efforts are essential to track population trends and guide management and recovery efforts. With the installation of a fish monitoring station in the Feather River near Oroville, DWR can more accurately track the arrival timing, number, species, and origin (natural or hatchery raised) of returning fish.

“The fish monitoring station is a valuable reporting tool for counting Chinook salmon and steelhead populations in the Feather River,” said Byron Mache, Environmental Scientist with DWR’s Division of Integrated Science and Engineering. “Accurate estimates allow DWR and its partners, like the California Department of Fish and Wildlife and National Marine Fisheries Service, to track the success of hatchery activities along with environmental and fishing impacts.”

Located approximately 6.5 miles downstream of the Feather River Fish Hatchery, DWR’s fish monitoring station is located near the bottom of the low flow channel, a section of the river that offers lower river temperatures and improved gravel habitat, making it a prime holding and spawning environment. As fish migrate up the river, they pass through a chute in the monitoring station that spans the river channel. The chute contains an underwater camera that captures video of fish using motion detection software.

DWR scientists review the video footage to determine the exact species of fish and can check to see whether the adipose fin has been clipped. A clipped adipose fin indicates that fish are of hatchery origin. Since the monitoring station was installed, DWR scientists have recorded more than 10 different fish species in the Feather River, including Chinook salmon, steelhead, Sacramento pikeminnow, hardhead, pink salmon, chum salmon, American shad, and striped bass.

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 August 26, 2025 are:  

• Spring-run Chinook salmon (April 16 through June 30): 17,754
• Fall-run Chinook salmon (July 1 through present): 733
• Steelhead: 203
• To see previous year data, visit CalFish.org.

Read more about the Feather River fish monitoring station on DWR’s blog and watch our YouTube video. Information about passing over the monitoring station is outlined in this DWR video.

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 12: Afterbay Dam Crest Road/Brad Freeman Trail south of State Route 162 to the East Hamilton Road Trail Access
• August 25-29, September 2-4, 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.

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.

Golden Mussel Inspection Program – Ramp Hour Changes

DWR is alerting water recreators to upcoming changes to boat ramp hours that will be in effect as of Monday, Sept. 1. Hours for inspection/decontamination services at the North Thermalito Forebay will remain the same. Additional changes to boat ramp hours are anticipated with the shortening days.

In addition, 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 10 p.m.  

Starting Sept. 1: Daily from 7:30 a.m. to 9 p.m.

• Spillway  
• Bidwell Canyon

Extended Ramp hours: Daily from 5 a.m. to 10 p.m.  

Starting Sept. 1: Daily from 5 a.m. to 9 p.m.

• Lime Saddle
• Loafer Creek

Thermalito Afterbay 

Ramp hours: Daily from 7:30 a.m. to one hour after sunset

Starting Sept. 1: Daily from 1.5 hours before sunrise to 1 hour after sunset

• Monument Hill

Thermalito Forebay

Ramp Hours: Daily from 7:30 a.m. to 7:30 p.m.

Start Sept. 1: Daily from 8 a.m. to sunset

• North Forebay (Non-motorized vessels only)

Current Lake Operations

Lake Oroville is at 823 feet elevation and storage is approximately 2.37 million acre-feet (MAF), which is 69 percent of its total capacity and 113 percent of the historical average.

Feather River flows are at 800 cubic feet per second (cfs) through the City of Oroville with 5,700 cfs being released from the Thermalito Afterbay River Outlet (Outlet) for a total Feather River release of 6,500 cfs downstream. Flows through the City of Oroville will reduce to 650 cfs by 9 a.m. on Saturday, Aug. 30. Flows through the Outlet will increase to 5,850 cfs by 11 a.m. with total Feather River releases remaining at 6,500 cfs. 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 8/28/2025.