A GRANGE — Nearly 1,200 adult spring-run Chinook salmon — originally released as part of the San Joaquin River Restoration Program — made their way to the Tuolumne River, where they found abundant habitat and cold, clean water in which to spend the summer prior to spawning in the fall.
This migration represents a milestone for the San Joaquin River Restoration Program and highlights the impact of the Tuolumne River Partners’ (Turlock and Modesto irrigation districts and the San Francisco Public Utilities Commission) management of the Tuolumne River.
TID, MID, and SFPUC announced in 2023 their joint $80 million habitat restoration program along the lower Tuolumne River, aimed at improving the health and long-term recovery of the fishery and local communities it serves.
The salmon, part of a long-term experimental reintroduction effort on the San Joaquin River, were drawn to the Tuolumne due to its robust spring pulse flows, favorable temperature conditions, and higher water volumes — conditions created under the Tuolumne River Partners’ annual operations to support fall-run Chinook.
As spring pulse flows receded and the La Grange Diversion Dam— an over-pour dam built more than 130 years ago — ceased overtopping, the plunge pool at the base of the dam became disconnected from the lower river, trapping a significant number there. In coordination with the U.S. Fish & Wildlife Service, California Department of Fish and Wildlife, National Oceanic and Atmospheric Administration fisheries, and consulting firm FISHBIO, the districts supported five relocation operations, moving spring-run salmon to deeper, cooler pools downstream to support their survival over the summer. District staff provided logistical and technical support that aided the relocation efforts.
“We were pleasantly surprised by the number of spring-run salmon identified in the Tuolumne River,” said Brad Koehn, TID general manager. “And it was impressive to see the way district staff and state and federal fishery agencies worked together — from CDFW designing the relocation plan to TID’s construction and maintenance team developing a device to safely relocate the fish from the pool at the base of La Grange Dam to a more suitable part of the river.”
Drone surveys of nine pools in the Tuolumne River on July 16 counted 1,154 fish. Biologists estimate that the total number of spring-run may be over 1,500.
“In addition to the pulse flow, numerous other factors, including large hatchery releases, extremely wet conditions during migration to sea, and closure of commercial fishing, all contributed to the unprecedented spring-run numbers seen on the Tuolumne in 2025,” said Andrea Fuller, vice president and senior biologist of FISHBIO.
Thirty years ago, TID, MID and SFPUC entered a settlement agreement with Tuolumne River Trust and other parties to help restore the Tuolumne River fall-run Chinook salmon population.
By 2030, project partners are hoping to develop 77 acres of suitable salmon rearing and floodplain habitat, and add approximately 100,000 tons of gravel in specific areas for optimal salmon spawning and rearing.
The Tuolumne River is nearly 150 miles long, originating inside Yosemite National Park at 13,000 feet elevation. Water from the Tuolumne irrigates more than 200,000 acres in Stanislaus County and provides drinking water for more than 2.7 million Bay Area residents.
