The dam that holds back Nicasio Reservoir needs repairs, and the state has given the Marin Municipal Water District until Tuesday, December 1 to explain how it will fix it.
The California Division of Safety of Dams downgraded Seeger Dam from "satisfactory" to "fair" after finding that the earthen dam's underdrains, water stops, spillway reinforcement, anchorage and foundation are not performing as required under modern standards. The agency notified MMWD of the downgrade in May 2026.
The reservoir serves as part of the water supply system for more than 190,000 people in southern and central Marin County, including San Rafael. About 75% of MMWD's water comes from local reservoirs on Mt. Tamalpais and in west Marin.
Engineering Director Alex Anaya told the Marin Independent Journal on July 26 that the rating does not signal an immediate threat. "The concern is really under those rare or really extreme hydrological or seismic events," Anaya said. Under the state's rating system, "fair" means no safety deficiency exists under normal operating conditions. A "poor" rating would require corrective action; "unsatisfactory" would trigger emergency repairs.
The project is expected to take eight to 10 years, Anaya said. The district is seeking an engineering consultant to develop the plan, which will require a design alternatives analysis and coordination with multiple agencies for permits and environmental review.
The state order traces back to 2017, when the Oroville Dam spillway failure in Butte County prompted regulators to evaluate dams of similar construction statewide. MMWD's first phase of evaluation ran from 2017 to 2021 and led to repairs of surface defects, subdrain cleaning, and crack sealing. A second phase, approved in March 2022, used ground-penetrating radar for deeper structural analysis. That report went to the state in 2025.
In addition to Seeger Dam, Peters Dam at Kent Lake and the dam at Soulajule Reservoir have been under state scrutiny since 2017. Seeger Dam is one of seven dams MMWD operates; six are earthen structures built of soil, clay and natural materials.
At a Tuesday, July 21 board presentation, member Matt Samson asked whether the state was comfortable with the eight-to-10-year timeline. Staff said it mirrors other projects statewide. General Manager Ben Horenstein told the board that if regulators saw an imminent concern, they could go as far as ordering the reservoir drained. He characterized the order as maintenance work with a clear directive to develop a plan and get moving.
Samson said he wanted staff to use the project as a chance to strengthen the dam beyond minimum requirements. Board member Ranjiv Khush agreed, saying he hoped for improvements that would ensure the spillway's stability far into the future.
Nicasio Reservoir holds 22,340 acre-feet of water. MMWD had previously considered a separate project to install an inflatable rubber gate on the spillway to boost capacity, but withdrew that plan due to high costs and regulatory complexity.
MMWD's board meets on the first and third Tuesdays of each month at 6:30 p.m. The next scheduled meeting is Wednesday, August 5. The district must submit its repair plan to the state by Tuesday, December 1.
