Lake Oroville Update - September 11, 2026

Feather River Floating Classroom

Feather River Floating Classroom raft tours are returning this fall! Sponsored and developed by DWR, the Floating Classroom program guides participants through Feather River spawning habitat while DWR and Pacific States Marine Fisheries Commission scientists describe Chinook salmon conservation efforts supported by the State Water Project. Discussion topics include ongoing and planned research, restoration and monitoring projects, and fisheries management activities.

Free floating classroom tours start Sunday, Sept. 27 during the Salmon Festival weekend, followed by tours each Saturday between Oct. 3 and Nov. 7. Each weekend will have two public tours with limited seats. Tickets will be released each Friday, approximately two weeks in advance of each tour, and are available on a first-come, first-served basis with up to four free tickets available per person each fall. Reserve your FREE floating classroom ticket(s) on Eventbrite.

Well Project Ongoing Near Thermalito Afterbay Dam

The Thermalito Afterbay is a 57,000 acre-foot, off-stream reservoir contained by the Thermalito Afterbay Dam and is part of DWR's State Water Project facilities in Oroville. Construction on the Afterbay began in 1966 and was completed in 1967. It stores water that flows through the Thermalito Pumping-Generating Plant during power generation and provides controlled releases to the Feather River and irrigation water to over 150,000 acres of local farmland.

The need for managing seepage at the Afterbay was recognized during planning, design, and construction. Beginning in 1957, groundwater levels were measured and recorded to establish data for comparing pre- and post-Afterbay conditions. With the initial filling of the Afterbay reservoir in 1967, additional water percolated into the aquifer causing groundwater levels to rise downstream of the dam. DWR installed 15 shallow wells spaced 1,000 to 3,000 feet apart to manage groundwater levels in the upper aquifer. The original installed wells are at the end of their service life.

Work is underway on Phase II of DWR's Thermalito Afterbay Well Replacement project, which is replacing six wells along Highway 99. This project concludes replacement of the remaining operational wells that were not replaced during the Phase I project in 2008. DWR anticipates completing well drilling in October with plans to resume construction work next year to finish the installation of pumps, motors, piping, and electrical equipment. DWR continues to measure, record, and monitor groundwater levels downstream of the Afterbay Dam weekly to ensure the ongoing safety of the facility.

Caution Advisory Issued for Lake Oroville's Middle Fork

DWR has issued a caution advisory for Lake Oroville's Middle Fork due to a visible algal bloom between Bean Creek Bar and the inlet near Bald Rock Canyon. DWR staff are collecting samples for laboratory analysis. A caution advisory will remain in place until the bloom dissipates.

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 harmful.

• 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.

Take these precautions in affected Middle Fork areas for your safety:

• Swimming is allowed but stay away from algae and scum in the water and on the shore.
• Do not drink lake water or use it for cooking.
• Do not let pets and other animals go into or drink the water or eat scum on the shore.
• For fish caught here, throw away guts and clean fillets with tap water or bottled water before cooking.
• Do not eat shellfish from this water.

DWR's environmental scientists routinely monitor for blue-green algae and their toxins within the Oroville-Thermalito Complex. Regular monitoring occurs during the summer months with water samples taken at various locations, 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.

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 September 5, 2026, are:

• Spring-run Chinook salmon (March 4 through June 30): 8,509
• Fall-run Chinook salmon (July 1 through present): 7,133
• Steelhead: 41
• To see previous year data, visit CalFish.org.

Current Lake Operations

Lake Oroville is at 776 feet elevation and storage is approximately 1.85 million acre-feet (MAF), which is 54 percent of its total capacity and 92 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 5,850 cfs for a total Feather River release of 6,500 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 9/10/2026.