Water District Clarifies Details of Hydraulic Fluid Release at Ruth Dam

Stock photo of Ruth Lake [Photo taken on November 22, 2024 looking south from the dam. Image from Rick Currier]

The district said the sheen was observed on Ruth Lake near the R.W. Matthews Dam intake structure and is currently contained within floating booms placed around the area. District staff surveyed the lake and reported finding no evidence of oil along the reservoir shoreline.

The district also clarified the timeline of the incident.

According to the district, a mechanical failure occurred March 3 during a routine inspection by the California Division of Safety of Dams. The failure involved the hydraulic system that operates a slide gate at the dam’s intake structure. The district says it activated its Emergency Action Plan and notified dam safety regulators and other required agencies the same day.

During diagnostic work over the following week, hydraulic fluid leaked from the operating system into a flooded cylinder room inside the intake structure. The enclosed space sits about 110 feet below the lake surface and contains non-flowing water.

On March 11, a sheen was observed on the surface of Ruth Lake near the intake structure. District staff deployed absorbent pads and containment boom and reported the release to the National Response Center, the California Governor’s Office of Emergency Services and the North Coast Regional Water Quality Control Board the same day.

The district estimates that about 15 gallons of hydraulic fluid leaked into the cylinder room during diagnostic work. It is not yet known how much of that fluid reached the lake surface.

District officials say the lubricant used in the system is Clarion Green BIO-32, a plant-based hydraulic fluid designed for equipment operating underwater in reservoirs. According to the district, the product is biodegradable, minimally toxic to aquatic life and does not bioaccumulate in the food chain.

Officials say no impacts to fish, wildlife or water quality have been observed, and the incident does not pose a risk to drinking water supplies.

Ruth Lake sits roughly 75 river miles upstream of the district’s diversion facilities near Essex, where water is drawn from the Mad River aquifer. The Humboldt Bay Municipal Water District supplies drinking water to approximately 90,000 residents in Eureka, Arcata, Blue Lake, McKinleyville, Manila, Fieldbrook-Glendale and Humboldt.

Containment measures remain in place at the dam. According to the district, multiple booms and absorbent materials have been deployed around the intake structure and downstream of the dam while staff monitor conditions and conduct water sampling at the request of the North Coast Regional Water Quality Control Board.

A commercial dive contractor is expected to inspect the hydraulic system and begin repairs next week. The scope of repairs will depend on what is discovered during the dive inspection.

Redheaded Blackbelt’s initial report relied on a Trinity County news release and a hazardous materials spill report filed with the California Governor’s Office of Emergency Services. The district’s public statement provides additional detail about the location of the oil, the equipment involved and the sequence of events leading to the sheen observed on Ruth Lake.

Read the full Humboldt Bay Municipal Water District release, click the following:
2026-03-12_RWMatthews_PS

Earlier: Damage at Ruth Dam Releases Hydraulic Oil to the Mad River which Supplies Water to Areas of Humboldt County