Marin Water and the County of Marin are preparing to lower Phoenix Lake ahead of the 2026 winter season, creating additional storage capacity to capture stormwater and help reduce flood risks in San Anselmo and Ross during early winter storms.
Marin Water is scheduled to begin pumping October 26, following pump modifications from October 19-23. Pumping is expected to continue into mid-November, with weather conditions and water quality guiding decisions about when to conclude operations.
During an October 2021 storm following a drought, Phoenix Lake's lower water level allowed the reservoir to capture runoff that otherwise would have flowed into Ross Creek and Corte Madera Creek. Lowering the lake before this winter could create similar storage capacity, although the benefit will depend on the timing, intensity and duration of storms and water levels when rain arrives.
Marin Water retains responsibility for all operating decisions. Marin Water General Manager Shaun Horne said: "Our responsibility is to provide safe, reliable drinking water, and that will always guide our operational decisions." However, the effort cannot eliminate flooding in San Anselmo or Ross, and residents and businesses should continue preparing their properties and emergency plans.
The initiative brings together the County's flood risk reduction expertise and Marin Water's reservoir management capabilities, serving more than 191,000 people in central and southern Marin County, as part of broader winter preparedness efforts.