PREVIOUSLY

• No Risk to Local Water Supply After Hydraulic Fluid Leak at Ruth Lake Dam, Water District Says

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The Humboldt Bay Municipal Water District has completed emergency repairs to a hydraulic gate at the R.W. Mathews Dam on Ruth Lake, according to a press release issued today. 

Environmental containment and cleanup operations have also been wrapped up following a March 3 failure in the dam gate’s hydraulic operating system. The subsequent discovery of a hydraulic fluid leak triggered “an all-hands emergency that demanded immediate action to protect our community’s water supply,” District General Manager Michiko Mares says in the press release.

No oil was observed in the Mad River at any point during the incident or repair operations, according to the district.

When we reached Mares on the phone this morning, she said while the total cost of the multi-agency repair effort yet to be fully calculated, the district’s expenses will likely be “several hundred thousand dollars.” At its March 12 meeting, the district’s Board of Directors approved an initial expenditure of up to $350,000 from the capital reserve fund, and that amount didn’t factor in the as-yet-undetermined costs of environmental disposal.

These costs could result in a rate increase for customers, though Mares said, “[W]e are hopeful that this [incident] will fall under our insurance claim and we can recoup the majority of costs incurred.”

She went on to highlight the community-wide repair efforts, saying she’s thankful that local residents and agencies come together to solve hard problems.

Here’s the district’s press release:

EUREKA, CA — Humboldt Bay Municipal Water District (District) has completed emergency repairs to the hydraulic operating system for the slide gate at the R.W. Matthews Dam intake structure on Ruth Lake in Trinity County. The slide gate — which releases the primary water supply for approximately 90,000 Humboldt County residents — is fully operational, and environmental containment and cleanup operations at the reservoir have been concluded. No oil was observed in the Mad River at any point during the incident or repair operations.

“This was an all-hands emergency that demanded immediate action to protect our community’s water supply,” said Michiko Mares, General Manager of Humboldt Bay Municipal Water District. “From the moment the hydraulic operating system failed on March 3, our team and our partners worked around the clock — diagnosing the problem, mobilizing a dive crew to a remote reservoir, and executing repairs while protecting the lake environment. I could not be prouder and more appreciative of the people who made this happen.”

The Incident

On March 3, 2026, during a routine Division of Safety of Dams (DSOD) field inspection, the hydraulic operating system for the slide gate at the Ruth Dam intake structure failed while being operated resulting in a loss of the District’s ability to control releases from Ruth Lake.

The District immediately activated its Emergency Action Plan and Situation Evaluation Committee, and notified state and federal dam safety regulators. Over the following week, District staff conducted extensive diagnostic testing to determine the cause of the failure.

On March 11, a sheen of hydraulic oil was observed on the lake surface near the intake structure. The oil — Clarion® Green BIO 32, a plant-based, readily biodegradable hydraulic fluid specifically selected by the District for use in a public water supply reservoir — had leaked from the hydraulic system into a flooded equipment room inside the intake structure. The District immediately deployed containment booms and notified the National Response Center, Cal OES, the North Coast Regional Water Quality Control Board, the California Department of Fish and Wildlife (CDFW), and Trinity County Environmental Health, among other agencies.

The Response

The District’s Board of Directors convened on March 12 to declare an emergency and authorize emergency procurement under Public Contract Code §20645 and 22050. Within days, the District had mobilized an 8-person commercial dive team from Associated Underwater Services, Inc. (AUS) of Spokane, Washington, along with a specialized environmental contractor, Patriot Environmental Services, Inc., to manage containment and cleanup on the lake.

Dive operations began March 17 at the intake structure. Over the course of four days, divers entered the intake structure and the hydraulic cylinder room, identified a disconnected hydraulic line as the primary cause of the hydraulic operating system failure, and restored the gate to operation via a temporary hydraulic line.

Following closure of the gate, District staff dewatered the penstock and entered the cylinder room to perform additional inspections and hydraulic system repairs with support from Daveco Hydraulics and Welding. Permanent repairs to the hydraulic operating system were completed on Sunday, March 22, 2026, restoring full operational capability. All environmental controls were removed on March 24, 2026.

Environmental Protection

Throughout the response, the District maintained an extensive containment and monitoring program in coordination with the California Department of Fish and Wildlife, Office of Spill Prevention and Response (CDFW OSPR), which directed the environmental response. Environmental controls included:

• Oil-only containment booms around the intake structure and dive area

• Secondary containment booms between the spillway walls

• Absorbent booms upstream and downstream of the dam

• Boats equipped with absorbent materials for immediate deployment

• Continuous visual monitoring during all dive and repair operations

• Water quality sampling at multiple locations on Ruth Lake and the Mad River at the direction of the North Coast Regional Water Quality Control Board

Toluene testing requested by the Regional Water Quality Control Board returned non-detect results at all sampling locations, confirming no contamination of the lake or river.

The total volume of hydraulic oil released and recovered during the incident and repair operations was approximately 44 gallons. All recovered oil and contaminated absorbent materials were collected and disposed of by Patriot Environmental Services through licensed waste disposal in accordance with applicable regulations. Containment booms were removed on March 24, 2026, following post-work monitoring that confirmed no additional oil was surfacing. No oil was observed in the Mad River at any point during the response. No impacts to fish, wildlife, or water quality were observed.

Acknowledgments

The District extends its gratitude to the many partners whose rapid response and sustained commitment made this emergency repair possible.

The District’s operations and maintenance team, led by Director of Operations and Maintenance Dale Davidsen, provided on-site coordination throughout the emergency, from initial diagnostics through final repairs. District staff maintained environmental controls, operated the hydraulic power unit during dive testing, completed the final repair, and ensured continuous communication with regulators and contractors.

Associated Underwater Services, Inc. (AUS) of Spokane, Washington, mobilized an 8-person dive crew and equipment to a remote mountain reservoir on short notice and executed a complex, multi-phase inspection and repair at 110 feet of depth under challenging conditions.

Patriot Environmental Services, Inc. of Sacramento, California, provided on-water and onshore containment, cleanup, and waste disposal support throughout the operation.

Daveco Hydraulics and Welding of Eureka, California, provided specialized hydraulic repair expertise during the penstock-access phase of repairs.

GR Sundberg, Inc. of Arcata, California stood ready with siphon installation materials and a work plan as a contingency to ensure continued water supply downstream of the reservoir.

Humboldt Sawmill Company provided necessary parts on short notice so we could complete the critical repair.

The California Department of Fish and Wildlife, Office of Spill Prevention and Response (OSPR) provided on-site oversight during dive operations and directed environmental containment, monitoring, and cleanup operations on the lake.

The Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC) maintained close coordination with the District throughout the emergency, receiving daily progress updates during active dive operations.

The North Coast Regional Water Quality Control Board directed water quality sampling and provided regulatory oversight of the District’s environmental controls.

Trinity County Environmental Health coordinated local response efforts and maintained communication with the public.

The District’s Board of Directors acted swiftly to declare the emergency and authorize the resources necessary to protect the community’s water supply.

Looking Ahead

The District will incorporate findings from this emergency into its long-term inspection, maintenance, and emergency preparedness programs for R.W. Matthews Dam. The incident has underscored the importance of maintaining emergency response capabilities for critical submerged infrastructure and the value of pre-positioning relationships with specialized contractors who can mobilize on short notice. The District will continue to work closely with DSOD, FERC, and other regulatory partners to ensure the ongoing safety and reliability of R.W. Matthews Dam and the community’s water supply.

“Ruth Lake is approximately 75 river miles upstream of where we divert water to serve Humboldt Bay communities,” said Mares.

“Protecting this reservoir is not just our job — it is our mission. The response to this emergency reflects the strength of the partnerships between our District, our contractors, and the regulatory agencies that oversee dam safety and environmental protection in California. These are our #WaterHeroes.”